2325: That's just about it from me after another superb day of action from the ATP World Tour Finals at London's O2 Arena. Hope you enjoyed it and thanks for your contributions. Cheerio!

2320: After having to put up with three days of my ramblings, Mark Ashenden jumps into the hotseat on Wednesday. He will provide text coverage of both matches, which you can also follow on BBC Radio 5 live sports extra. Although their coverage of the late match will not start until commentary of Hull City against Everton in the Premier League has ended.

2315: Wednesday sees the return of Group B, with Novak Djokovic facing Robin Soderling in the afternoon session and world number two Rafael Nadal taking on Nikolay Davydenko in the evening.

2310: Despite his victory, Federer is still not 100% certain to reach the semi-finals. If he loses his final match to Juan Martin del Potro both players will have two wins to their name, while Murray will also have two wins if he beats Fernando Verdasco. If Verdasco beats Murray and Federer beats Del Potro then Federer will advance alongside one of Murray, Del Potro and Verdasco. If any players finish with the same win/loss ratio, the deciding factor will be number of sets and games won.

2300: After such a promising start, Murray will be bitterly disappointed to have let the match slip from his grasp. In the end it was a comfortable victory for Federer, who has now won each of his past two meeting with Murray but trails 6-4 in the career head-to-head. The win means Federer is guaranteed to finish 2009 as world number one so he will enter January's Australian Open as the top seed.

Anon via text on 81111
"If Murray is ever going to win a Slam he has to get out of this habit of playing most of the match defensively, it doesn't work against the best players."

Federer 3-6 6-3 6-1 Murray
From the moment Federer broke to go 4-1 ahead, Murray displayed the body language of a beaten man. A flurry of unforced errors from Murray hand Federer a match point but the Scot saves with a volley that skims the baseline and gets game point when Federer flicks a lob just long. The world number one pulls Murray back to deuce on four occasions - once with a sumptuous forehand crosscourt winner that leaves Murray swinging at thin air. Murray smashes his strings against his right hand; the Scot knows the game is almost up. Murray goes long to concede a second match point but Federer nets a routine forehand. A third match point arrives for the 28-year-old and on this occasion Murray nets. Game, set and match Federer.

Federer 3-6 6-3 5-1 Murray*
Oh dear. Murray nets, Federer sends down an ace, Murray nets, Federer sends down an ace. Murray now serving to stay in the match.

*Federer 3-6 6-3 4-1 Murray
Groans of anguish reverberate around the O2 Arena as Murray nets a backhand to give Federer another break point. The Scot comes into the net aggressively and seems to be in control of the point. But Federer retrieves a ball deep into the forehand court and Murray sends a straightforward volley agonisingly long. It's a double-break to Federer Murray's first-serve percentage has plummeted. Curtains for the British number one?

Federer 3-6 6-3 3-1 Murray*
Murray will have to make more of an impression the Federer serve on the Swiss will coast to victory. Come on, Andy.

BBC Radio 5 live sports extra's David Law Tweeting from the O2 Arena: "Amazing match this between Murray and Federer. James Auckland confirms on 5 Live Sports Extra that Murray does Karaoke."

*Federer 3-6 6-3 2-1 Murray
Chip and charge, chip and charge, chip and charge. Federer is all over the Murray serve like a blanket and brings up 15-40. Two break points are saved but Federer takes the third and that is a massive break.

Federer 3-6 6-3 1-1 Murray*
Doesn't it annoy you when someone can perform one truly amazing sporting manoeuvre after the next with effortless ease? Federer is one such individual and it makes for incredible viewing. He looks in the mood to go on and win this but it would be criminal to write Murray off.

*Federer 3-6 6-3 0-1 Murray
It's not advisable to open the deciding set with a double fault, is it? Fear not. Murray takes the initiative and after Federer sends a lob over his head, the Scot scampers to the back of the court, spins and sends a sensational backhand crosscourt passing shot beyond Federer at the net. The 28-year-old has come to the net 30 times thus far, winning 22 point in the process.

Federer 3-6 6-3 Murray*
What a game. Two of the game's top stars playing at something approaching the peak of their abilities. Federer is a picture of concern as Murray takes him to deuce and appears to have the momentum. Murray can't believe a backhand has been called out and challenges, unsuccessfully. Federer gives him verbals across the net before serving out the set. We're heading for a decider.

BBC Sport's Oliver Brett Tweeting from the O2 Arena: "Couple in front of me at o2 getting abuse for whispering between points. Weird."

*Federer 3-6 5-3 Murray
"Some players play better when they're angry," says David Law on 5 live sports extra before a bubbling Murray storms into a 40-0 lead. Federer gets a point back but the game is Murray's.

Federer 3-6 5-2 Murray*
It looks like Murray's about to break straight back as he out-foxes Federer to bring up 0-30. Federer turns it around to 40-30 before Murray makes deuce. The world number one brings up game point with the most delicious pick-up you could ever imagine and then sees out the game when Murray fails to control a return. Murray berates the umpire about something. "You've been stopping me in my last four service games," says Murray. "Why are you looking at me like I'm an idiot?" Not sure what all that was about. Wolf whistles galore as Murray changes shirts at the turnaround. Murray will now serve to stay in the set.

*Federer 3-6 4-2 Murray
The standard of tennis has been raised by several notches. This is massively engrossing. Federer takes the initiative from the outset and, although Murray does little wrong, a pinpoint volley gives the Swiss two break points. He takes the first in majestic fashion by wrong-footing Murray with an inside-out forehand. A joy to behold. Federer has broken serve.

Federer 3-6 3-2 Murray*
Really clever stuff from Federer. He interchanges serves into the body with serves kicked out wide. Murray looks angry and belts a forehand return straight at Federer, who takes evasive action and holds serve to love. James Auckland on 5 live sports extra telling the world about Murray's liking for a bit of the old karaoke. The Scot's fans will be singing from the rooftops if their man wins this.

*Federer 3-6 2-2 Murray
Murray secures a fairly comfortable hold and twizzles his racquet with delight. Federer's going to hate that.

BBC Sport's Piers Newbery on Twitter: "Good effort from Murray in 1st set, loving the edge to this match. Fed needs to be 100% sharp or Murray's normal game wins. Mince pie time..."

Federer 3-6 2-1 Murray*
In sharp contrast to Murray's last service game, Federer is untouchable and holds with aplomb. Huge boos ring out around the O2 Arena... not for Federer or Murray but at the sight of Tottenham Hotspur football players Jermain Defoe, Robbie Keane and Michael Dawson on the big-screen TVs.

*Federer 3-6 1-1 Murray
Make no mistake about it, there is certainly some needle between Federer and Murray tonight. Former British professional James Auckland on 5 live sports extra has just told a story of when all of the top players were at an event some time back and Federer shook the hand of every player apart from Murray. Very interesting but back to the action... the world number one pushes hard for a break of serve and Murray struggles to contain his opponent's laser-guided groundstrokes. Federer crafts a succession of classy winners but repeatedly stunts his own progress with uncharacteristic lapses in concentration. The Swiss twice goes long and fails to hide his frustration as Murray levels the set.

Federer 3-6 1-0 Murray*
Ideal start to the second set for Federer, who closes out game one with a perfectly-timed ace. I should have mentioned something earlier... if Federer beats Murray today he will be guaranteed to finish 2009 as world number one. He is already the first player to finish in the top two for seven consecutive years.

Tim Henman on BBC 3 on playing against Murray: "I didn't like playing him as my game didn't match up to his, but I'm glad to say that I beat him the last time I played him."

*Federer 3-6 Murray
Two aces help Murray to 40-0. Federer challenges the first but it's well in, while the second skids through off the surface at a worryingly low trajectory. Federer saves one set point and then a second when Murray tightens up and double-faults. The Swiss then dispatches a weak second serve with a forehand winner to make deuce before Murray comes up with a ace kicked out wide to bring up a fourth set point. This time Federer goes long and wide with a forehand and Murray takes the first set.

Federer 3-5 Murray*
I'd love to be able to drive-volley my way to game point and then see it out with a deft volley at the net after a serve kicked out wide. That's exactly what Federer just did. man's a bit special.

*Federer 2-5 Murray
Having worked so hard to force a break of serve, it seems a shame Murray falls 15-40 down the following game. The crowd reaction may indicate a break back is inevitable but try telling Murray he's a beaten man. The Scot saves both break points, the second with a 134mph ace into the far corner of the service box. He then completes the comeback when Federer fires into the tramlines. Critical hold for Murray.

Federer 2-4 Murray*
There is a reason why Murray is one of precious few players who can get under Federer's skin. It's because on the court he cares not a jot for the 28-year-old's reputations and has technical skills and a doggedness that frustrates the life out of him. Murray races to 0-40 when Federer doubles faults and then puts a top-spin forehand long. The 15-time Grand Slam winner saves one break point but then goes wide and Murray bounces around the backcourt with delight. That's the break. The Scot's fist-pumping and yelps of "C'mon" seem to be annoying Federer big time.

*Federer 2-3 Murray
They may have in the past, but nobody can suggest Murray's game lacks aggression tonight. He really is taking it to the world number one out there. Unfortunately, he is up against a guy who is probably the greatest player of all time. The Swiss fights his way to deuce but miscues to hand Murray the game.

Federer 2-2 Murray*
Solid as they come. Federer holds comfortably and, after a frenetic start to proceedings, both players have now settled on serve.

Andrew Castle on BBC 3: "That's a useful two games for Murray, first the break and then a big hold."

*Federer 1-2 Murray
Federer attempts to draw errors out of Murray by teasing him with the sliced backhand but the world number four is no mug. Despite dropping his first game, Murray looks really sharp out there and holds to 30.
I wrote earlier that the BBC 3 TV coverage would be streamed through the BBC Sport website. I was wrong. Apologies.

Federer 1-1 Murray*
A hugely impressive response from the 22-year-old Scot. Federer claimed before last week that he had devised a gameplan to beat Murray and that, from now on, their matches would be played on his terms. These two have previous and there is definitely some spice in the air. Murray shows outstanding movement, accuracy and timing to break back at the first time of asking. With Federer stranded at the net, Murray passes the great Swiss with a crosscourt backhand. Federer has now lost his opening service game in each of his first two matches.

*Federer 1-0 Murray
Murray gets his first service game off to a poor start when he frames the ball out of the court (it cannons into the overhead scoreboard). The Scot, dressed in blue top, matching shorts and white trainers, sends down a double fault, goes wide and then nets to hand Federer an immediate break of serve. Dreadful start from Murray. Federer playing with bucket-loads of aggression.
* Denotes next to serve.

2058: Hold on to your hats. We're under way!

2057: As Caroline reports, both players receive a huge ovation. This is comfortably the best pre-match atmosphere we've had all week. The 17,500 spectators inside the Arena know this is huge. Federer wins the toss and elects to receive.

Annabel Croft on BBC Radio 5 live sports extra: "I would go out of my way to see this guy (Federer) play and I hope he continues to play for a long while yet."

BBC Sport's Caroline Cheese Tweeting from the O2 Arena: "Whoah. Big cheer for Murray. But massive roar for Fed. Where's the partisan crowd? Cracking atmos tho."

2050: And here's what world number four Murray has to say: "He's the greatest player of all time. I've played well against him in the past so I'll try to do the same again. I'll play to win tonight and we'll see what happens."

2048: Some pre-match thoughts from 15-time Grand Slam champion Federer: "It's always special when the top guys play each other, especially at the ATP Tour finals because you play each other earlier than at other tournaments. We've had some great matches over the years so we'll see how this finishes. I've got to be aggressive. The surface is slow and the most attacking player will probably win."

2046: This match is being screened live on BBC 3, you can listen to it on BBC Radio 5 live sports extra and, needless to say, receive live updates right here.

2042: Murray knocked Federer out of last year's end-of-season tournament in Shanghai and another victory today would guarantee the British number one and world number four a place in the semi-finals. A win for Federer would do the world number one a world of good but he may still have some work to do to reach the last four.

Andy Murray on Twitter: "Chilling in the locker room. See you all in a bit."

2037: On an occasion like this, I can but urge you to play your part in the action by text to 81111,606 or Twitter

2035: Federer and Murray have met nine times in the past. Murray has won six and Federer thee; Murray four of the past five and Federer the most recent match in Cincinnati in August.

2032: Forget about the Champions League football - unless, of course, you want to read Jonathan Stevenson's superb text commentary - because tonight is all about the tennis.

2030: The waiting is over. It needs no introduction. Roger Federer against Andy Murray in the ATP World Tour Finals at London's O2 Arena. Can you think of a more enjoyable way to spend your Tuesday evening?