1600: So Federer goes through to the semis but who is going to join him - Murray or Ferrer? Two men in contention for one place. We'll know the answer after - or maybe even during - today's evening match between Murray and Ferrer at 2000 GMT. I'll be back for that, in the meantime why don't you have a read of Piers Newbery's report from the O2?

1555: "To play against Robin is never easy, he's a big hitter and you have to work on your defence," says Federer after extending his head-to-head record against Soderling to 15-1. "He can be very frustrating, but I took it to Robin and I'm very pleased to have won."

BBC Sport's Piers Newbery tweeting from the O2 Arena: "Very classy stuff from Federer as he wins 7-6 6-3, ominously good by the end. @andy_murray just needs a set against Ferrer. No problem...."

1545: For those of you keen to avoid a permutations nightmare - and for Federer and Murray - that was a good result. It means Murray only needs to win one set against Ferrer to finish second in Group B and join Federer in the semi-finals. If Murray loses, he will be level with Soderling and Ferrer on one win apiece and they will be separated by percentage of sets won. It's now mathematically impossible for Soderling to go through but Murray and Ferrer are still in the hunt. Got it?

Federer 7-6 (7-5) 6-3 Soderling
Cool as you like, Federer saunters through his final service game and, before we know it, he's shaking hands with Soderling at the net. Wife Mirka is congratulated by O2 season-ticket holder Diego Maradona and his female companion. Game, set and match Federer. Through to the semis as Group B winner. Soderling's place in the competition now hanging by a thread.
* denotes NEXT to serve

Federer* 7-6 (7-5) 5-3 Soderling
And there it is - the crucial break for Federer. The Swiss gets to 30-30 for the second game running and this time attacks the Soderling serve before dishing up a gorgeous forehand winner. Federer seals the break and will now serve for the match.
* denotes NEXT to serve

1537: "Jon from London (see 1505) seems pretty sure Murray will win a set tonight. Murray is not through yet & Ferrer isn't going to lie down. No player wants to play in t he finals & leave without a win. He's going to give it his all."
Barry in Belfast via text on 81111

Federer 7-6 (7-5) 4-3 *Soderling
This time Soderling manages a couple of points on his opposite number's delivery, but the body language isn't amazing and he struggles to launch a genuine challenge as Federer pulls away and maintains his advantage of sorts.
* denotes NEXT to serve

Federer* 7-6 (7-5) 3-3 Soderling
Federer wants this done and dusted asap but he'll have to wait a little longer. The Swiss looks well placed for the break at 30-30 but there's a strong finish from Soderling, who rushes in to volley a winner and seal the service hold.
* denotes NEXT to serve

pottiella on 606: "No lack of trying from Rog... decent match... more tactical than intensive...."

Federer 7-6 (7-5) 3-2 *Soderling
No let-up from Federer as he chalks off a hold to love. He could see Soderling breathing deeply after an energy-sapping game four and decided to twist the knife. Cruel, very cruel.
* denotes NEXT to serve

Federer* 7-6 (7-5) 2-2 Soderling
Testing times for the Tibro native. Federer's all over his serve to get to 30-30 and then again to force deuce. A truly woeful backhand finds the foot of the net to give Federer break point but the big man saves it with an ace down the 'T' and then smashes his way two advantage. A mammoth rally follows in which Soderling appears in control until Federer, at full stretch, gets one more return over the net and the Swede goes horribly wide with his pick-up at the net. But some gigantic serving pulls Soderling to safety and he eventually emerges when Federer lashes a backhand into the net.
* denotes NEXT to serve

Federer 7-6 (7-5) 2-1 *Soderling
Stunning angled backhand winner keeps Soderling snapping at Federer's coat-tails but the world number two keep his neck in front with a lovely backhand pass up the line. Andrew Castle on BBC 2 says Murray is now guaranteed a place in the semi-finals if he beats Ferrer at 2000 GMT.
* denotes NEXT to serve

BBC Sport's Piers Newbery tweeting from the O2 Arena: "He can still qualify but even tougher for Soderling now he's dropped the first set, and Hawkeye then denies him a break in the second. Ouch..."

Federer* 7-6 (7-5) 1-1 Soderling
Convincing reply from Soderling and, lest we forget, the Swede is still very much alive in this competition. For now, anyway.
* denotes NEXT to serve

Federer 7-6 (7-5) 1-0 *Soderling
Big scare for the newly-crowned Group winner. Soderling gets to 30-40 on his opponent's serve and that means a break point. The Swiss sends a searing forehand up the line and it's called good. Federer may hates Hawk Eye but he's not complaining as he uses it to prove Soderling shot was actually out. Danger averted, Federer holds with an ace.
* denotes NEXT to serve

1505: "I don't want to criticise the tournament organisers too much, but I have tickets for tonight and if Roger wins 2-0, then the Murray match becomes almost meaningless as barring a huge loss to Ferrer, Murray is through. These two matches should've been switched."
Jon in London via text on 81111

Federer* 7-6 (7-5) Soderling
A couple of terrific rallies but everything goes with serve until 2-2, when Federer constructs a brilliant point before opening his body and drilling a forehand across court. Will Robin make it? Yes but he can only find the net. Mini break to Federer and he races to 5-2. Two solid points give Soderling hope at 4-5 and Federer then squanders a set point at 6-4. But at the second time of asking, the world number two comes through - but only after Soderling inexplicably opts to leave a volley that lands in. Silly boy. Federer qualifies from Group B as group winner.
* denotes NEXT to serve

Federer 6-6 *Soderling
Soderling cranks up the pressure and fights his way to 30-30, but then chucks a forehand into the tramlines and looks to the heavens (or the O2 roof) in frustration. Federer closes out with an ace to give us Group B's first tie-break. Who's gonna blink first?
* denotes NEXT to serve

Federer* 5-6 Soderling
Fine time to come up with a love service hold, closed out by the Swede with an unreturnable bullet of a first serve.
* denotes NEXT to serve

Federer 5-5 *Soderling
A trademark backhand winner up the line draws the biggest cheer of the day and puts Federer on course for 40-0. A slight blip follows but nowt major and Soderling fires long to hand over the game. I could watch that one-handed backhand again and again.
* denotes NEXT to serve

Federer* 4-5 Soderling
Tibro's finest is very much back in this. Holds serve to 15 and, yes, out come the fist pumps. This time with gritted teeth as he glares at his support team. Andrew Castle on BBC 2 reminds us that Robin is the only man to have beaten Rafa Nadal at the French Open. Ever. What a claim that is. Fed now serving to stay in the set.
* denotes NEXT to serve

Federer 4-4 *Soderling
Federer opens with his second double fault. Is there hope yet for RobSod? The Swede wastes his advantage by netting an easy groundstroke for 15-15 but Fed puts a forehand half-volley a couple of inches wide, sends another into the net and loops a third beyond the baseline. Soderling breaks back and it's all to play for again.
* denotes NEXT to serve

BBC Sport's Piers Newbery tweeting from the O2 Arena: "An early break for Fed and that might get a little cheer in the Murray household. Lots of krayzee Swiss fans in today..."

Federer* 4-3 Soderling
Another fine service game from Soderling but it's time to add to his collection of only four points on the Federer serve - he's got to do something or he's heading out. Crowd pretty muted.
* denotes NEXT to serve

Federer 4-2 *Soderling
A first double fault for the world number two but it fails to halt his progress. A cheeky dabble lands on the sideline for game point and Federer wraps it up when Soderling drills into the net.
* denotes NEXT to serve

Federer* 3-2 Soderling
Superb response from the big 26-year-old. Races to 40-0, drops a point but gets over the line and there's another fist-pump in the direction of his support team. However, first-serve percentage of just 44% for the Swede right now.
* denotes NEXT to serve

Federer 3-1 *Soderling
Hold to love for the man in red. Closed out when Soderling nets a backhand. Ruthless from Federer, break converted.
* denotes NEXT to serve

Federer* 2-1 Soderling
Federer's turn to apply the pressure in what is the pair's 16th meeting. The masterful Swiss works his way to deuce and all of a sudden Soderling looks nervous. As does his fiancee Jenni Mostrom in the stands. Federer engineers a break point and Soderling opts to attack the net. Fed drills in his return and Soderling can't control his forehand volley at the net. It drops into the trams and Federer has an early break of serve.
* denotes NEXT to serve

Federer 1-1 *Soderling
Tough opener for Federer, that. Some MASSIVE hitting from Soderling forces the 29-year-old Swiss to retreat. He's pinned back to the baseline, scampering left and right to return his opponent's bombs. The fourth seed, coached by Magnus Norman, forces deuce by a couple of wayward groundstrokes enable Federer to come through.
* denotes NEXT to serve

1417: "So how does it work, depending on who wins this one what does Murray need to do to go through?"
Alan via text on 81111
If Federer wins, he's through and Murray only needs to win one set against Ferrer to join him. If Soderling wins, Murray must win or he's out. If Soderling and Murray win, they will be level with Federer on two wins, so will be separated by percentage of sets won and then percentage of games won. Clear? No, thought not.

Federer* 0-1 Soderling
Smooth as you like from the big Swede. Early fist-pumps as he holds to 15 with a commanding service hold. Precious little not to like about that game. Sealed with a forehand winner.
* denotes NEXT to serve

Anne Keothavong on Twitter: "What's the deal with Soderling's shirt?? Mind you, he's not the only one this week who's come out on court in a dodgy shirt at the O2..."

1412: Loads of permutations of what can happen today. Ten alternatives, to be precise. More on that in a mo because the players are ready to go - and it's Soderling get us going in a garish yellow number...

Times tennis correspondent Neil Harman on Twitter: "Is it just me or do the MC's plummy introductions at the O2 really grate?"

1407: Let's hear from world number two and 16-time Grand Slam champion Federer... "The important thing is to play well and feel good, no matter how you look at it. This year is pretty straightforward for me - if I play well I should be through. He's improved a lot over the last couple of years and I've had to make a few adjustments. I have to play aggressive against him indoors and that's what I'll try to do,". And what world number four and two-time French Open finalist Soderling had to say: "I feel good, I've enjoyed every match I've played against him. I've improved with each match this week and hopefully I can continue to improve today."

1405: First up it's Federer against Soderling. Both men have just emerged through the dry ice at the O2. Massive ovations all round. Big day for you guys, too. So make sure you get involved in that chat - by Tweeting me @bbcsport_david, text in on 81111 (UK) or +44 7786200666 (worldwide) with TENNIS before your message, or dipping into the 606 message boards. Sound OK?

1355: Roger Federer. Andy Murray. Robin Soderling. David Ferrer. Four into two doesn't go. It's make-or-break Thursday in Group B at the ATP World Tour Finals. By the the end of today we will know two of our four semi-finalists. Let's get it on...