Live Commentary: Roger Federer vs. Stanislas Wawrinka - as it happened

Hello, and welcome to Sports Mole's live coverage of the match between Roger Federer and Stanislas Wawrinka at the ATP World Tour Finals.

Ever since the first ball was struck in this tournament, all the talk has been about a potential Novak Djokovic versus Roger Federer final and so far, it's looked nothing but a near certainty that the pair will clash on Sunday. Earlier today, Djokovic fulfilled his part of the bargain by defeating Kei Nishikori but in 10 minutes time, Federer will attempt to join him. There's a small matter of Australian Open champion Stanislas Wawrinka standing in his way, though.

The two Swiss haven't got long to go until they are joining forces to try to win the Davis Cup for their nation but tonight, they are bitter enemies for what has the potential to be an enthralling encounter. Federer oozed class during the group stages while Wawrinka regain a bit of the form that saw him win his first major title at the start of the year.

Only a couple of places separate them in the world rankings but it's a different story when you take a glance at the head-to-head record. Wawrinka has defeated the man he calls "The Boss" just twice in 16 meetings, with both wins coming on clay. He has competed with the world number one on other occasions but never quite gotten over the finishing line.

Both players have just about completed their warm-up. Both players look confident and settled but we will see if that lasts over the course of the next couple of hours. It will be Federer to serve first.

Wawrinka takes the opening point of the contest but two attempted slice returns are off target. The Swiss number two then makes another error before Federer sweeps in to put away a one-two off a first serve.

Wawrinka kicks off his opening service game with an accurate serve out wide but he goes for too much on a backhand down the line to make it 15-15. Federer capitalises on a net cord for 15-30 but misses out with what seemed to be a routine backhand down the line and that's enough to concede the momentum to the Swiss number two who holds to 30.

BREAK! Both players possess excellent backhands and they are on show during a high-quality rally from the baseline. It's Wawrinka who prevails and an error from Federer gifts his opponent a 15-30 advantage. There is a lot of power on show from Wawrinka right now and it earns him a break point which is taken with a huge cross-court forehand!

It's worth noting that is the first time that Federer has been broken all week. Anyway, onto Wawrinka's attempt to consolidate his breakthrough and two heavy serves earn him 30-15 but a stray backhand gives Federer a chance. Wawrinka holds on though with an ace and forehand into the corner. He's overpowering Federer at the moment.

This is probably a must-win game for Federer in regards to remaining competitive in the set and he does so comfortably enough, defying a Wawrinka backhand return to hold to 15.

Back-to-back aces from Wawrinka see him take a 30-0 lead and although Federer prevents a third, he can't get enough on the return to get it over the net. Over-confidence sees Wawrinka attempt a crazy drop shot but it's a minor blip as he holds with a baseline winner.

BREAK! More hard-hitting tennis from Wawrinka earns him the opening point but Federer regains control at 30-15. However, some ridiculous ball-striking off his backhand wing earns Wawrinka 30-30 and he has a break point when Federer hits the tape with a forehand. WOWZERS! Wawrinka middles a return with his forehand straight into the corner of the court for the double break.

BREAK! Better from Federer, who hangs tough with Wawrinka from the baseline to establish a 0-30 advantage. He has a shot at a second-serve return too, but it goes into the net. But, a double fault from Wawrinka gifts his compatriot two break points. Wawrinka looks nervous, and it shows as he pummels a forehand long of the baseline. This set isn't over.

Wawrinka has 0-15 and after returning a smash, has a chance at 0-30 but he can only hit the net with the passing shot. Two big first serves take Federer to two game points and he moves to within one game of his opponent when Wawrinka hits a return into the net.

SET! Wawrinka is yet to lose a point behind his first serve and that continues for the first point, but a double fault suggests to Federer that the nerves are still present. However, two well-directed serves bring up two set points for the Swiss number two, which he takes with a smash and a volley at the net. First blood to the Australian Open champion.

That was a terrific set of tennis played in the best atmosphere of the week. More of the same for set two please.

Wawrinka opens the second set with a classy backhand into the corner but he twice goes long of the baseline to give his opponent the advantage and the former world number one comes through comfortably.

There are encouraging signs from Federer at the start of this set and he makes up plenty of ground to lead 15-30. The six-time winner of this event does nothing with a backhand return off a second serve before completing miscuing a backhand. That brought a frustrated reaction from the 33-year-old. It's Wawrinka's game when he connects with a backhand that Federer hits into the net.

It's clear that Wawrinka has the power to beat Federer tonight but he needs to use it wisely. A forehand winner earns him 0-15 but he over-hits a backhand return to allow Federer to get to 30-15 before he holds with a good serve out wide.

Clever from wawrinka who mixes his play up with a serve-and-volley for 15-0 before following it up with an ace down the middle. His next serve-and-volley attempt sees him picked off by Federer but two returns can't find their way back into court and we are back on level terms.

It's a game of missed opportunity for Wawrinka who has control of a couple of rallies before eventually losing them. At 40-15, Wawrinka outwits Federer at the net to remain in the game but he misses with the backhand down the line to allow his fellow Swiss to hold serve.

Wawrinka's in trouble when two wayward shots off the ground go long but he halves the deficit when Federer mis-hits an attempted top-spin forehand. However, a third baseline shot off target gifts Federer two break points but Wawrinka shows superb composure to get back to deuce. That concentration deserts him with what seems a routine forehand conversion to give Federer a third opening, but again, he hits his way to deuce for a second time. An ace from Wawrinka - his sixth of the match - earns him game point and he takes it when Federer nets a return. Big let off for the world number four.

Federer looks in control at 30-15 before Wawrinka executes a stunning backhand pass to put Federer under pressure at 30-30. But what a response from the 33-year-old, who is in the perfect place to out away a backhand volley. The game isn't over though and Wawrinka hits a second backhand pass for deuce. The next point is unreal with both men throwing everything at each other but Wawrinka blinks first when going long down the line. Federer hangs on for the hold and we remain on serve. Both men are getting a little twitchy though now.

It's getting to the critical part of the set and it really could go either way. Federer is definitely playing more aggressively though and pressure at the net draws the error from Wawrinka for 15-15. The next two points are shared for 30-30, but it's game point Wawrinka with an easy volley at the net. It takes him a number of attempts but Wawrinka holds to put the pressure back on Federer.

What pressure? A big serve is hit long by Wawrinka before Federer ghosts in to convert a volley. A wayward forehand from Wawrinka concedes three game points but the Swiss number two blazes a winner down the line. It's game to Federer, though, who whips a serve out wide that is hooked wide by Wawrinka.

Wawrinka swats away a volley to ease the tension inside the O2 Arena before an ace out wide takes him to 30-0. He should have three game points but a shocking volley finds the net and a double fault leaves Federer two points from the set. The six-time winner has a look at a second serve but he hits the tape and it's Wawrinka's game when he finds the target with a forehand down the line.

In next to no time, Federer has three game points and a love hold is complete with a serve and volley. There's no pressure coming from Wawrinka on the return.

SET! It's a nightmare start from Wawrinka who misses with a routine volley and he can't react fast enough to stop one from Federer. It's 0-30, and that becomes 0-40 when Wawrinka sends a smash into the net. It's a disastrous error and Federer breaks to love when Wawrinka dumps another shot into the tape.

BREAK! Wawrinka makes a blistering start to the set to earn 0-30 but there is drama here. Federer wanted to challenge a call that has given Wawrinka three break points but it wasn't heard by the umpire and can't be made. He's not happy. He saves the first, but he will be furious now - Federer goes long and Wawrinka has the early break.

Actually, let's clear that up. Federer didn't realise that he lost the first point and he shouldn't have done. The ball went out and he thought the umpire had called it out. Massive talking point.

Wawrinka shows a deft touch at the net for 30-15 but he miscues a shot from the baseline to give Federer a sniff. The door is slammed shut on him though and Wawrinka consolidates the break.

You can see the anger boiling inside Federer but he needs to move on. He does so effectively in this game, quickly holding to 15.

Federer's frustration quickly turns to encouragement when a Wawrinka backhand is directed wide for 15-30 but Wawrinka responds with a solid first serve down the middle. He maintains the momentum to come through with the hold and Federer only has three chances remaining to break back and get back into this match.

Federer comfortably gets to 30-0 but Wawrinka is back in the game when he smashes a backhand into the body of his opponent. It was taken in good spirits though. The next shot might not be though as a forehand passing shot from Wawrinka clips the net and goes in for 30-30. The Swiss number one holds on for 2-3 but he still has plenty of work to do.

Federer should have 15-15 but some solid defensive work from Wawrinka results in Federer netting a smash. A return then goes long for three game points for Wawrinka and a love hold is sealed with a serve out wide.

Wawrinka wants this done and dusted as soon as possible and a backhand winner down the line gives him 0-30. Federer needs an immediate reply here. He's fortunate when another backhand from Wawrinka just clips the net but he serves with more authority to level the score. Federer not's prepared to give this match up and he comes through after Wawrinka had brought up deuce.

Now then. Two errors from Wawrinka give Federer 15-30 and the former world number one senses his opportunity. Wawrinka gets back to 30-30 but he blazes a forehand wide of the line and it's break point to Federer! Wawrinka saves it but Federer goes on the attack to set up a routine smash and he has a second chance to level this up. Wawrinka survives though with a very gutsy hold and he's one away from the final.

Federer remains aggressive but Wawrinka hits back to bring a mistake out of his opponent for 15-15. Federer brings up two game points but Wawrinka fires back with some quick hand skills at the net to remain in the game. Wawrinka has a look at a second-serve return but it goes marginally long and he will have to try to serve for the match.

BREAK! Federer must win this game but he goes inches long with a mis-hit backhand to concede the opening point but Wawrinka responds with a mistake of his own. Wawrinka regains the lead with a big serve, but he hooks a forehand wide and things are getting incredibly nervy now! It's MATCH POINT to Wawrinka after Federer nets a backhand. Can he convert? He can't! Federer survives with a forehand down the line with Wawrinka stranded at the net and it soon becomes break point when Wawrinka goes long. Wawrinka breathes again when coming out on top in a titanic tussle from the baseline and he has match point number two with a volley at the net. He makes another mistake but has a third chance when Federer slices long. What a game! He finally makes a first serve but Federer smashes it back and wins with a forehand. After saving three match points, Federer has another chance to break and this one is taken when Wawrinka nets. What drama!

This match continues to deliver as Wawrinka drills two winners past Federer for 0-30. Where were those in the last game?! Wawrinka gets to two break points but they are both saved by Federer, who really has the grit between his teeth, and he holds with a heavy forehand into the corner.

Wawrinka starts a must-win game with a forehand winner but a wild double fault levels the score. Another mistake from Wawrinka leaves Federer two points from the match but wawrinka holds his nerve to move to game point, which is taken when Federer nets.

Federer takes the opening point of the tie-break with a backhand pass that leaves Wawrinka flailing at the net and the mini-break is taken when he wrong-foots Wawrinka on the baseline. Wawrinka looks hurt but it might just be cramp. He takes the next point with an aggressive backhand. Federer moves 3-1 ahead when a Wawrinka lob goes wide but it's back on serve when Wawrinka middles a backhand into the corner. Federer takes a 4-2 lead at the change of ends when a forehand loops onto the line but he had little control on that shot.

The two-point margin remains as both men fire down big first serves but that becomes 5-4 when Federer goes long with a backhand. We are back on serve and Wawrinka claws his way back to 5-5 when Federer makes another error. This is as dramatic as it gets. A match point is coming up after the next point. Who for though? Wawrinka! Federer nets a second-serve return. Can he get over the line at the fourth time of asking. No! A return goes long and we continue.

MATCH! Federer holds his nerve at the net to bring up match point for the first time of the match, but it's on the Wawrinka serve. It doesn't matter though - Federer wins! A superb drop volley gets the job done.

What an incredible match. This tournament has needed one like that for the past week! You have to feel sorry for Wawrinka, who missed out on four match points, but Federer showed unreal resolve to move through to a final with Novak Djokovic tomorrow night!

On that note, we are bringing our coverage to an end but we will be back at 5.45pm tomorrow evening for all of the buildup ahead of what should be an epic occasion! Goodbye for now.