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

The countdown has already started in London's O2 Arena. The players are making their way out to an expectant crowd. Stanislas Wawrinka is the first man out to generous applause, but I think the reception for Rafael Nadal might be on another level...

Yup, I was right. I think that the roof has just come off the arena. Hopefully this encounter will live up to the entrances. If it does, we are going to be in for a corker.

Wawrinka has won the toss, and he has elected to serve first. The Swiss is going to need all the help that he can get this afternoon - he has never defeated Nadal in 11 attempts.

As well as being able to seal his place in the semi-finals with victory this afternoon, Nadal has the added incentive of knowing that a win will also see him end the year as the world number one. That was almost unthinkable when he missed the Australian Open at the start of the year after failing to recovery from a knee injury.

It won't be the end of the world for whoever loses today, They will have a second chance to qualify for the last four against either David Ferrer or Tomas Berdych on Friday. Those two players headline this evening's action after both lost their opener.

The two players are ready. Wawrinka has the ball in his hand, and he will serve first.

Super start from Wawrinka, who confidently completes a couple of one-twos off his serve, with Nadal sending the ball wide on the next point. What a backhand to complete the game, the ball flashing over the net and bouncing inside the tramlines.

Wawrinka struggles with his footwork on the first point, and that allows Nadal to capitalise, but there are no problems with the next, with the Swiss smashing a return winner past the left-hander. However, Nadal remains composed, and a first ace helps him get on the board.

Wawrinka overhits a backhand to open the game, but he responds with an excellent forehand winner. Nadal is attempting to wrong-foot Wawrinka when he can, but the Swiss manages to come through the game to 15.

Delightful from Nadal, who moves Wawrinka around the court before winning the point with a passing shot into the open court. A net-cord helps Wawrinka win a point, but that's all that he is getting out of this game. Uneventful start.

BREAK! Wawrinka makes two sloppy errors off his forehand wing, and Nadal has 0-30. A smash helps him halve the deficit, but he is soon facing two breaks points when he frames a shot from the baseline. He saves the first with an ace, but a double fault concedes the game in tame fashion.

You are kidding me! Wawrinka shows unreal touch to direct a backhand behind Nadal, but the left-hander stretches out to flick the ball back across court. It turns into a routine game for the world number one, and he consolidates the break won in the last game.

Wawrinka is struggling to stay with Nadal, but he finds the line to record an ace to get back to 15-30. The Swiss converts a volley at the net, but he goes long of the mark to offer another break point to Nadal. However, Wawrinka shows great spirit to take three points in a row and remain in contention in the set.

Now then, an opening for Wawrinka. Nadal makes a couple of mistakes, and out of nowhere, the Swiss has 0-30. However, Wawrinka goes for broke with his backhand and he hooks it wide, before a big Nadal first serve isn't returned. Wawrinka earns break point after a Nadal error, but he misses out when his shot clips the net and goes wide. WHAT A WINNER - Wawrinka crushes a forehand down the line and he has his second break point, but again, he misses out by going for too much on a return. Nadal eventually comes through the game, but he was asked plenty of questions by his opponent.

The opening two points are shared, before Nadal nets a second serve return to hand Wawrinka the advantage. The Swiss is growing into this match, and Nadal can't handle a 136mph serve to allow Wawrinka to take the game.

BREAK! Wawrinka comes out on top after a brutal rally, but Nadal drives down a powerful first serve to move level. The seventh seed then misses with an attempted forehand winner, and Nadal is two points away from the set. However, Wawrinka outlasts Nadal in successive rallies, and he has another break point. This time, he gets it! He is all over Nadal at the net, and he powers a forehand into the corner of the court. Game on!

The tide has well and truly changed here. Three points in a row and Wawrinka is 40-0, and a fantastic backhand volley on the stretch earns him the game. All of a sudden, Nadal is serving to stay in the set!

Nadal throws in a double fault at the start of the game, and he looks rattled. However, he sends down two first serves that Wawrinka can't return, and the Swiss miscues a backhand down the line. Two game points for Nadal, and he takes the first with another solid first serve.

Nadal captures the mini-break on the first point to move back into the ascendancy, and a Wawrinka error soon makes it 2-0. The Swiss grabs the mini-break back when Nadal marginally misses the line, and a third ace levels things at 2-2. This is impossible to call at the moment, and Wawrinka takes the lead. Nadal reaches the change of ends at 3-3 after an accurate serve to the body.

SET! The world number one pings down an ace to pile the pressure on Wawrinka, but the Swiss hits back with some aggressive play to get to 5-4. Wow, that was close. Nadal clips the line with a baseline shot and we have 5-5. Who will bring up set point? It's Nadal, whose defensive play is out of this world! That's so unfortunate for Wawrinka. He loses his footing at the net when he is about to put away a volley, and Nadal takes advantage and hits the forehand winner. Wawrinka is going berserk, and has been given a code violation warning.

I think that Wawrinka is going to struggle to come back from that, but we shall see. The Swiss's service and return stats were actually better than Nadal's during that first set. The pair trade mistakes during the first six points of Nadal's service game, before Wawrinka can't direct a half-volley over the net. The Swiss is then berating himself after driving the ball halfway up the net.

Wawrinka has complained to the umpire about Nadal apparently receiving advice from his coach. I will keep you posted. The Swiss's frustration helps him out during this game, and he rattles his way to a hold to love.

What a shot. Wawrinka jumps all over Nadal's wide serve and his backhand return finds the corner. Nadal then overhits a forehand, and his opponent has 15-30. The action is hotting up now, and Wawrinka earns two break points after winning a net exchange with Nadal. The Spaniard is firmly on the back foot, but Wawrinka is wilting on the big points. The break points come and go, and so does the game, after Nadal finds the line with a baseline winner and ace respectively.

BREAK! Wawrinka misses a sitter at the net to fall behind early, and he does the same with a routine forehand. The Swiss's game is falling apart, and after a backhand goes wide, Nadal has three break points.The Spaniard misses with the first, but Wawrinka gifts him the advantage with a forehand error. Is that the beginning of the end for the seventh seed?

Wawrinka looks encouraged when he gets to 30-30, and he looks even happier when Nadal goes long with a backhand, which was called out but actually clipped the line. Nadal didn't challenge, and Wawrinka has break point. However, the Swiss blasts a forehand return long, and the moment quickly passes. Nadal is two games away from confirming his world-number-one status for the remainder of 2013.

A must-hold game coming up for Wawrinka, and he begins well in easing into a 30-0 lead. That quickly becomes 40-0 when Nadal skies a return, and a hold to love is complete when Nadal nets.

BREAK! Wawrinka is having mixed joy with his aggressive approach. a couple of heavy forehands hit the mark, but he is still blazing plenty of chances wide. However, he has two break points after Nadal drives a backhand into the tramlines, and he converts when he volleys off the top of the net and into the open court.

Wawrinka is quickly beginning to dominate proceedings, and a peach of a forehand down the line earns 30-0. An unreturned serve makes it 40-0, but he just misses the baseline an attempted winner. It doesn't prevent the Swiss taking the game though with a serve-and-volley.

Nadal needs to hold here, because he has rapidly become second best. He lights up the crowd with a smash with his back to the net, but he goes on to the lose the point. It's 30-15, which soon becomes 30-30 when Nadal misses a routine forehand. What is going on?! The Spaniard almost goes long on the next, but he survives to take the point, and the game is his when Wawrinka blasts the ball into the net. Wawrinka will return to try to save the match.

Wawrinka plays a wonderfully-timed backhand smash to get back to 15-15, and he survives when Nadal misses with an attempted winner down the line. The Spaniard just can't find his timing right now, and quickly concedes the game.

That's more positive from Nadal, who steps into court to put away a volley, and he repeats the shot on the next point. The confidence in his shots is definitely beginning to return, but there's little he can do when Wawrinka hits a cross-court return off a second serve. Wawrinka strikes back once more with a booming 95mph backhand, but Nadal closes out the game by whipping a forehand into the corner.

Wawrinka starts the game with a flat serve down the middle, but a sloppy volley at the net allows Nadal to level. What a response from the Swiss, who flicks a half-volley just over the net, but Wawrinka throws in a double fault. It's 30-30, and a mammoth rally, Wawrinka outlasts Nadal to earn game point, which he takes with a huge ace out wide! We are into another tie-break.

That's a brutal forehand from Nadal, finding the corner with superb accuracy, and he takes the mini-break when Wawrinka goes long. He then powers a forehand yards over the baseline, and Nadal is 3-0 ahead, but what a response from Wawrinka, who sends a backhand winner down the line. I'm pretty sure that Nadal is foot-faulting on serve, but it is going unnoticed, and he moves to 4-1 with another baseline winner. Wawrinka needs this point, and he gets it with a winner down the line.

A serve out wide takes Wawrinka to 4-3, but like earlier in the set, it was out and Nadal failed to challenge. The Swiss is fighting so hard in this breaker, and he powers a forehand into the open court for 4-4, before Nadal goes long. Wawrinka has the mini-break! He is also two serves away from the set, but he goes wide on the first. What drama. It's 5-5, and we have either a set point or match point coming up. Which will it be? IT'S SET POINT TO WAWRINKA, after the Swiss finds the line with a forehand. What bottle from Nadal. He sets up the point beautifully before converting the smash.

Nadal finds a first serve and Wawrinka can't return. IT'S MATCH POINT TO NADAL, and he takes it! Wawrinka nets and Rafael Nadal will end 2013 as the world number one.

As two-set matches go, that was pretty special. You have to feel sorry for Wawrinka because that is probably the best that he has ever played against Nadal, but it wasn't good enough. He hit 30 winners during the two sets, but he also made 45 unforced errors, and that was ultimately the difference.

As for Nadal, that should seal his place in the semi-finals, and it also ensures that he will end the year as world number one.

That will be all from Sports Mole for this match. Thank you for joining us, and we hope that you return for David Ferrer's match with Tomas Berdych later this evening. Goodbye for now.