2203: Thanks for joining me online tonight. Highlights of the Old Firm game will be available later on this evening, while those for the St Johnstone-Aberdeen game will be online on Thursday. Good night!

2202: Rangers manager Walter Smith says he cannot comment on El Hadji Diouf's red card - a second booking for dissent - because he did not see what happened.

2200: We are hearing from reporter Chick Young that Sasa Papac is sitting up and talking - the Bosnian, you may know, was stretchered off after heading Kris Commons' shot off the goal-line.

2159: From Luke in Plymouth by text on 80295: "Rangers fan here, ashamed of the guys tonight. Don't know why they just collapsed discipline-wise, got a lot to answer for."

2157: The Scottish Football Association will no doubt have something to say about the 13 yellow (or was it 12?) and three red cards.

2155: From Lewis in Aberdeen by text on 80295: "I texted earlier telling you Neil Lennon needed to set a better example for his players and angrily confronting Ally McCoist is just pathetic. It's no wonder Scottish football isn't held in high regard with behaviour like this."

2150: From Hugh in Prestonpans by text on 80295: "Old Firm man of the match for me is Calum Murray. Who'd want to be a ref? Hope you lot praise him."

2148: I've seen some bad-tempered Old Firm matches before - that one was full of rage. Let's hope the fans keep cool on the way home.

2147: El Hadji Diouf went over to the Rangers fans and, despite police and stewards trying to prevent him from doing so, threw his shirt into the supporters.

2145: While all that was going on, Rangers assistant manager Ally McCoist and Neil Lennon, the Celtic boss, go eyeball to eyeball and have to be separated. What a mess!

2145: El Hadji Diouf is red carded after the final whistle! That's three sent off for Rangers.

Madjid Bougherra is shown a second yellow card and is sent off by Calum Murray. He reacts badly to the decision, though, and seemingly tries to push the card back in the ref's pocket!

2140: Beram Kayal concedes a late free-kick 25 yards from goal. Diouf curls it into the arms of Lukasz Zaluska.

2139: Rangers need a miracle. They simply have not been able to test the Celtic goalkeeper Lukasz Zaluska. Their best chance has been that misplaced header by Celtic defender Charlie Mulgrew.

2137: There are five minutes of injury time at Celtic Park.

2136: Charlie Mulgrew and Kris Commons line up a free-kick, which the former hits well but Allan McGregor makes a comfortable save.

2135: A miscue from St Johnstone striker Stevie May is sclaffed a yard wide of the right-hand-post from 15 yards out.

2134: Steven Davis makes a counter-attacking run down the right, but his looping cross is hit just beyond the reach of El Hadji Diouf.

2133: Gregg Wylde heads the ball off the goal-line. Rangers are pinned back.

2132: At what point do Rangers press the gamble button and push a player or two further up the pitch? They're leaving it late!

2130: From PtheT by Twitter #BBCSportsound: Re 2120. "A domestic treble of losing all competitions? Now that is optimism! #BBCSportsound."
Low blow, PtheT!

2128: There may have been a shout for a penalty in Perth as David McNamee decks Saint Johnstone forward Peter MacDonald as they jump for the ball in the Aberdeen box. Time is running out for an opening goal here.

2127: Celtic are in possession but Rangers are defending manfully. The Light Blues have 10 minutes to find a goal.

2125: Rangers right-back Ricky Foster defends well against Emilio Izaguirre and although the ball clearly comes off the Celtic player last, the home side are awarded a corner. Foster and Madjid Bougherra are raging!

2124: A good chance for the Dons to open the scoring in Perth is prevented by St Johnstone's Steven Anderson who slides the ball away from Aberdeen striker Sone Aluko - he was just about to pop the ball into the net.

2122: Kris Commons goes hurtling after a challenge by Steven Davis, who picks up a booking.

2120: From mickstuup on Twitter #BBCSportsound: "Rangers would still be in the hunt for a different treble, Keir, although I know that's being optimistic."
Aye, fair shout. That would be some achievement.

2119: "One-nil is always a precarious lead. All it takes is one goal for it all to turn around." A word of warning for Celtic from BBC Radio Scotland pundit Gordon Smith.

2118: Steven Davis is back on his feet and the match is under way again. How do Rangers press Celtic back with only 10 men?

2116: Credit to Beram Kayal, who sportingly knocks the ball out of play after his challenge on Rangers midfielder Steven Davis leaves the Northern Ireland star on the turf.

2115: Gregg Wylde shows he has decent pace as he makes a raid down the left for Rangers.

2114: St Johnstone's Liam Craig drives through the middle of the Aberdeen defence and bursts through on Dons keeper Jamie Langfield who makes a great save for substitute Nikola Vujadinovic to hook the ball off the line.

2112: That would have sealed it for Celtic, I reckon. Rangers need to get the next goal or their treble dreams are over.

2111: Georgios Samaras gets goal-side of Kyle Bartley and digs a low shot that comes crashing back off the foot of Allan McGregor's left-hand post.

2110: Both teams are looking sharp and dangerous and it has to be said that if it wasn't for three great saves from Aberdeen keeper Langfield, Saint Johnstone would be ahead." BBC Radio Scotland pundit Billy Dodds at McDiarmid

2109: Celtic midfielder Ki Sung-Yueng rifles a shot from 30 yards that fades just outside Allan McGregor's post.

2108: Rangers have half an hour to find an equaliser.

2107: Celtic's Gary Hooper comes back on to the field after receiving treatment.

2106: Madjid Bougherra shows the better side of his game, dispossessing Georgios Samaras and making a run up the right side of the pitch, but Ki Sung-Yueng slides in to break up the move.

2105: Celtic's number 88 is struggling after that challenge.

Madjid Bougherra runs his studs down the back of Gary Hooper's leg and is booked by Calum Murray.

2103: A brilliant run from Peter MacDonald, who drags the ball inside, leaves two Dons players standing, flicks the ball to Collin Samuel and he nods the ball onto the top of the Aberdeen goal. Still goalless in Perth.

2101: "We have to credit both defences. It's the only reason why we haven't had a goal at McDiarmid." BBC Radio Scotland pundit Billy Dodds

2100: Celtic defender Charlie Mulgrew miscues a header towards his own goal and Lukasz Zaluska has to scamper back to clutch the ball on his goal-line.

2059: Peter MacDonald sends a lovely ball to Saint Johnstone team-mate Collin Samuel only for Dons defender David McNamee to move in from a wide position to work a miracle intervention to prevent the goal.

2058: Sasa Papac is stretchered off. Let's hope he's OK. That was an almighty blow to the head from Mark Wilson's shot. Young Gregg Wylde comes on in his place.

A heroic goal-line clearance by Sasa Papac cannot keep Celtic out. Mark Wilson blasts a right-foot shot from 12 yards that the Bosnian heads clear but the ball falls for Wilson again and with his left-foot he knocks a shot into the turf and it bounces into the net.

2053: At McDiarmid Park, there's more pressure from St Johnstone as a free-kick given against Aberdeen defender Andrew Considine is struck by Danny Grainger but is headed just over the bar for a corner.

2052: Rangers send on Kyle Hutton for John Fleck. Celtic begin the second half.

2049: Possible change for Rangers - Chick Young is hearing that Gregg Wylde could be coming on for John Fleck.

2048: The players are coming back on to the pitch at McDiarmid Park.

2045: "You get your challenge wrong, you are booked." BBC Scotland pundit Gordon Smith feels sympathy for Steven Whittaker for his first booking, but believes he was foolish to go in for the tackle on Emilio Izaguirre that led to his second yellow card.

2043: From bainser77 by Twitter: "Stuck on a train relying on #BBCSportsound updates, last update was '2011: In Perth, Peter MacDonald is lively'. Match can't be that bad??"
It's not that bad, bainser, but unfortunately my colleague's computer is! Hopefully normal service will resume for the second half.

2041: "The first one wasn't a booking, the second one was." BBC Radio Scotland pundit Chick Young assesses Steven Whittaker's two yellow cards.

2036: There's trouble in the tunnel at Celtic Park! El Hadji Diouf seemed to want to exchange pleasantries with Scott Brown and then appeared to get into a tussle with Celtic coach Johan Mjallby. The other Rangers players do their best to usher the Senegalese to the dressing room.

2034: The South Korean dusts himself down, composes himself...and smacks a shot six inches over the bar.

2033: Steven Davis trods on the boot of Ki Sung-Yueng and Celtic have a free-kick in a very dangerous area in injury time.

2031: Referee Calum Murray shows a yellow card to Rangers midfielder John Fleck for a rash challenge on Beram Kayal.

2029: I think I need my eyes tested. Scott Brown is booked yet it was the Celtic man who was on the receiving end of a crack on the shin from David Weir.

2027: Maurice Edu is slack with a backpass and his error is pounced on by Georgios Samaras, who shoots from 10 yards - Allan McGregor makes a great save with his legs.

2026: Calum Murray has words with Ally McCoist and gestures high in the stand as the place where the Rangers assistant boss will be watching the game if he does not cool his jets.

2024: What's El Hadji Diouf doing?! The Rangers striker went over to the Celtic dugout to remonstrate with Neil Lennon, Ally McCoist is hauled back by manager Walter Smith. Diouf is booked.

2022: Rangers midfielder Steven Whittaker is sent off for a second bookable offence, this time for a challenge on Emilio Izaguirre.

2021: El Hadji Diouf is clattered in a tackle by Daniel Majstorovic.

2019: Emilio Izaguirre - not unlike soul legend Jackie Wilson, anyone? - skins Ricky Foster out on the left wing, cuts back on to his right and sends a cross into the Rangers box - Allan McGregor gathers.

2018: From Paul on BBC Sportsound's Facebook page: "Might get a shot on target soon. 23 mins and the talent and skill on show is incredible."

2016: Rangers look like a team who love to defend. It seems a risky strategy, though, as Celtic, you feel, will make the pressure count eventually. Of course, Rangers have plenty of experience in playing on the counter-attack.

2014: Steven Whittaker is booked by Calum Murray for a foul on Ki Sung-Yueng.

2012: Does it ever amaze you how some people have no interest in football and could not tell you that the Old Firm were playing a cup replay this evening? A friend of mine was once in a hospitality suite at Celtic Park and introduced himself to the guy sitting beside him. "Pleased to meet you - I'm Danny McGrain," was the reply. How can a guy in his late 40s not know who Danny McGrain is?!

2011: In Perth, Peter MacDonald is lively for the Saints again and from the left-hand-side of the penalty box, smacks a volley towards the near post which is just turned round the corner by Dons keeper Jamie Langfield.

2009: Celtic keep up the frantic pace and midfielder Ki Sung-Yueng arrows a left-foot shot from 30 yards that skims just over the Rangers crossbar. And the fans go "oo-oo-ooh", not like Dick Emery, but in a "that-was-close" sort of way.

2008: St Johnstone look dangerous once more as captain Jody Morris sends a shot goalwards from just outside the box but it's blocked by Aberdeen midfielder Paul Hartley.

2007: And more good defending by Bartley as he cuts across the rampaging Scott Brown just in time - the Celtic captain was in a good position to shoot.

2005: Celtic's Kris Commons wins a free-kick and curls it to the back post where Kyle Bartley guides the ball to safety. Good defending by the on-loan Arsenal man.

2004: But hang on, Maurice Edu streaks forward with purpose and heads into the Celtic box before his pass across the goal is swept clear.

2003: To give you some idea of how much Celtic are camped in the Rangers half, I swear I saw Beram Kayal with a rubber mallet and tent pegs down his socks.

2002: David Weir and Majstorovic dive to meet a Celtic corner and clash heads. Ouch!

2000: Celtic keeper Lukasz Zaluska gives his defence kittens, as he comes out of his goal unnecessarily - but Daniel Majstorovic heads the ball clear.

1959: The home fans roar their approval at the skill shown by Emilio Izaguirre to dispossess El Hadji Diouf.

1958: Georgios Samaras pokes an effort at goal but does not threaten Allan McGregor's Rangers goal.

1957: Mark Wilson is brought down by Rangers left-back Sasa Papac, having skilfully evaded a challenge by John Fleck. Charlie Mulgrew gets on the end of the free-kick but heads wide.

1955: "The first signs are that we are going to get a decent game here tonight." BBC Radio Scotland pundit Billy Dodds in Perth

1955: Mark Wilson pings a ball down the right wing for Georgios Samaras but the big Greek cannot catch it and Rangers have a goal kick.

1954: Some good early pressure from St Johnstone in the match at McDiarmid, though nothing to really trouble Aberdeen keeper Jamie Langfield.

1953: Celtic striker Gary Hooper test the pace of Madjid Bougherra. The home side are applying pressure already.

1952: "It has to be said the pitch has looked better." BBC Radio Scotland commentator Rob Maclean at McDiarmid Park

1950: From Craigeeez on Twitter: "There's another big game in Scottish Football tonight, Keir!! #AberdeenFC #StJohnstone #CluelessBBCJourno's #BBCSportsound."
Ha! I'll do my best, Craigeeez!

1948: Celtic win a corner thanks to the persistence of Georgios Samaras.

1948: The SPL game gets going at McDiarmid Park.

1947: We're under way at Celtic Park, though not yet at Perth.

1946: Celtic are playing a 4-4-2 formation, while Rangers go with a 5-4-1.

1945: David Weir leads the Rangers team along the Celtic line-up to shake their opponents' hands.

1944: We're almost at kick-off time. Woo-hoo!

1943: The Celtic fans are belting out You'll Never Walk Alone. Rod Stewart is in the main stand, looking very sharply dressed, it must be said.

1942: Both sides can realistically challenge for top six places as the split draws ever nearer, and seventh-place Inverness and eighth-place Hibernian have each played more games than both Aberdeen and St Johnstone.

1940: It's surely going to be a close game at McDiarmid Park. In the meetings between St Johnstone and Aberdeen this season, the away team has won 1-0.

1936: The winner of this evening's tie will face an away tie against Inverness Caledonian Thistle in the quarter-finals.

1934: Uh-oh. I used "referee" and "bear" in the same sentence! Bear...Teddy Bear...Rangers fan! It's a conspiracy! ..That's the sort of madness refs have to endure.

1933: Calum Murray is the referee at Celtic Park this evening. Let's hope no-one is mentioning his name tomorrow, except in praise. What a lot of pressure for one man to bear!

1932: Celtic won the last time the sides met in a Scottish Cup tie at Celtic Park - a 2-1 win in 2005 - but Rangers won an Old Firm Scottish Cup semi-final in the east end of Glasgow in 1998 during the final months of Walter Smith's first reign as Ibrox boss.

1931: Should Kris Commons score this evening, he will become the first player to score in three successive Old Firm games since Henrik Larsson in season 2000/01.

1930: RANGERS TEAM: McGregor, Foster, Weir, Bougherra, Papac, Bartley, Whittaker, Edu, Davis, Fleck, Diouf. Subs: Alexander, Healy, Kerkar, Wylde, Hutton.

1929: CELTIC TEAM TO PLAY RANGERS:
Zaluska, Wilson, Majstorovic, Mulgrew, Izaguirre, Brown, Ki, Kayal, Commons, Hooper, Samaras. Subs: Cervi, Juarez, Stokes, Rogne, Forrest.

1927: "It's nothing serious. He wanted to have a fitness test today but the medical staff were not keen on it." Ally McCoist believes the injury to Nikica Jelavic shouldn't keep the player out for long.

1925: Rangers assistant manager Ally McCoist admits the loss of Nikica Jelavic and Kyle Lafferty is a blow but he says he knows El Hadji Diouf is capable of playing up front on his own.

1922: ABERDEEN TEAM:
Langfield, McArdle, McNamee, Considine, Smith, Aluko, Hartley, Jack, Milsom, Vernon, Blackman. Subs: Howard, Vujadinovic, Young, Pawlett, Paton, Magennis, Anderson.

1921: ST JOHNSTONE TEAM NEWS TO PLAY ABERDEEN:
Enckelman, MacKay, Anderson, Gartland, Grainger, MacDonald, Morris, Davidson, Craig, Samuel, Invincibile. Subs: Smith, Maybury, Adams, Taylor, Novikovas, Reynolds, May.

1920: "Rangers are always dangerous. They play this system very well. We've got to try and take the game to Rangers. We have to find ways of breaking them down." Celtic manager Neil Lennon on Sportsound

1918: In the SPL, 10th-placed St Johnstone host Aberdeen, who are one place above them, separated only by goal difference though the Perth side have a game in hand.

1916: On BBC Radio Scotland, Celtic manager Neil Lennon tells Chick Young that he is tiring a bit of the Old Firm fixture with tonight's game being the fifth of seven this season.

1914: Rangers have made a fourth change to the team who put four goals past St Johnstone on Sunday without reply. David Healy drops out in favour of El Hadji-Diouf.

1912: Lukasz Zaluska will start in goal this evening in place of the suspended Fraser Forster. Zaluska's last derby appearance came as a substitute in Celtic's 2-1 win over Rangers towards the end of last season.

1911: If tonight's Cup replay is settled on penalties, it would be the first time in a major competition that Celtic and Rangers have decided the outcome of a match from the spot, although Celtic won the 1974 Dryburgh Cup final 4-2 on penalties.

1908: For Celtic, Georgios Samaras comes back in to the starting 11, along with Lukasz Zaluska and Ki Sung-Yueng.

1907: Defender Ricky Foster also comes in to the Rangers side, with Vladimir Weiss dropping along with Jelavic and Lafferty.

1905: Thanks for joining me here tonight. I hope you enjoy what's to follow. At Celtic Park, there has to be a winner, whether it's after 90 minutes, 120 minutes or penalties. No messing in the Scottish Cup, eh?

1903: Other news for the visitors to Celtic Park is that captain David Weir is back in the Rangers team, as is John Fleck.

1902: Bad news for Rangers fans - striker Nikica Jelavic is out with a hamstring problem and fellow front man Kyle Lafferty misses out with tonsillitis.

1901: Celtic and Rangers are set to contest the Scottish Cup fifth round replay in the east end of Glasgow. Also on tonight is the Scottish Premier League match between St Johnstone and Aberdeen.

1900: Let's get ready to ru-u-u-u-u-umbl-l-l-l-le!