Live Commentary: Roger Federer vs. Kei Nishikori - as it happened

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

Yesterday saw the two most one-sided games in the history of the ATP World Tour Finals take place at the O2 Arena, but you'd expect that it is going to be a completely different story this afternoon. This afternoon's two competitors are currently making their way onto court in front of another packed crowd in London.

Guess what? Roger Federer got another rapturous reception. Surprised? Of course you're not.

A couple of years ago, this would have been a guaranteed straight-sets win for Federer but times have changed. Federer may be maturing like a fine wine but Nishikori have developed at an incredible rate over the past 12 months to really establish himself in the upper echelons of the game. He may be lacking a Grand Slam or Masters Series title but his run to the US Open final has proven that he can be a match for anyone on hard courts.

As you can see above, this is the fifth meeting between the two players since their first encounter back in 2011. We can discount the match in Basel three years ago, but Nishikori holds the advantage in their last three meetings, including a comeback win in Miami earlier this year. He lost to Federer on grass in June, but the victory in Florida is the match that he will take confidence from and after he overcame Andy Murray on Sunday, he's going to fancy his chances of another triumph this afternoon.

The two players are ready to get the action underway. After winning the toss, it will be Federer to serve first. Game on!

Against Murray, Nishikori made a tentative start but he wastes no time here in hitting his way to a 15-30 advantage. Federer serves his way out of trouble, though, as the Japanese misses out with three returns in succession.

Quality stuff from Nishikori who swats away a forehand winner into the corner, but his double-fault issues arise again to allow Federer back into the game. It's not for long, though, and the US Open runner-up holds to 15.

Federer opens with a backhand drop volley but Nishikori replies with a flat backhand down the line. High quality play from both. Nishikori floats a return long to fall behind again, but two points in a row earn him break point. Federer saves it with his first ace of the day and he's forced to save another as Nishikori continues to impress early on. The Swiss eventually seals the hold but this is going to be a competitive scrap today - far more competitive than yesterday's contests combined.

BREAK! Nishikori is winning the majority of the baseline exchanges so far and that carries on at the start of this fourth game. The Japanese displays his incredible defensive skills to move 30-15 ahead but a second double fault gives Federer a chance, which he takes with a blistering cross-court forehand. Federer looks so sharp for a man of 33 and he runs around the ball to dispatch a forehand winner for the break.

Nishikori has a sniff of the immediate break back at 15-30 but another forehand winner into the corner gets the Swiss back on level terms. The multiple time Grand-Slam champion holds to 30 for a 4-1 lead but it's been much closer than the scoreline suggests.

A smart approach sees Nishikori take the first point, but he's in trouble at 15-30 after a successful challenge from Federer leads to a third double fault. The Asian superstar gets back to 30-30 but he sends a backhand down the line just wide to give Federer the chance of the double break. Nishikori survives though, and he remains competitive in this first set.

An ace registering just 113mph gets Federer off to the perfect start and another - his fourth of the match - earns three game points. A love hold is completed with a serve-and-volley and the Swiss moves one away from taking the opener.

Both players net tamely to take the score to 15-15 before Nishikori wrong-foots his opponent with a well-timed backhand down the line. The Japanese then picks off a volley for two game points before a backhand return from Federer floats long.

SET! A big first serve gets Federer on his way but this set is far from over and Nishikori benefits from a double fault to get to 15-30. He gets a look at a second serve on the next point but it's a sublime delivery from Federer to set up the forehand down the line. Another second serve forces an error from Nishikori to give Federer a set point, which is duly taken with a forehand into the corner.

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Like in his opening match with Andy Murray, Nishikori has undergone a bit of treatment on his wrist before the start of the second set but he is fit to continue.

Nishikori comes out firing at the start of the second, quickly putting together three points in a row before unleashing a backhand winner for the hold to love.

In next to no time, Federer completes his own hold to love to put the pressure back on his opponent.

BREAK! After the opening two points are shared, Nishikori's double fault woes come back to haunt him to give Federer 15-30. The Swiss then runs around a second-serve return to take control to bring up two break points. Big moments here. Nishikori saves the first when Federer goes long but Nishikori concedes the break when making a forehand error. It could be a long way back from here.

Nishikori takes the first point but he's making a few errors now - possibly due to his wrist niggle. Federer seals the game with an inside-out forehand and you feel as though Nishikori must hold here to have any chance of keeping pace with the legendary Swiss.

Nishikori makes another unforced error to concede 15-15 but he responds with a tasty backhand winner down the line. Federer's soon back on the offensive for 30-30 but he miscues a forehand down the line when it seems easier to make than miss. Nishikori completes an impressive hold when forcing his opponent off balance on the baseline.

Federer looks on the way to a comfortable hold before Nishikori finds the baseline with a tremendous lob that Federer had given up on retrieving. The exchange is a lengthy one but Federer prevails to maintain his stranglehold on the set and match.

BREAK! Nishikori deserves credit for continuing to battle away, despite potentially being hindered by a wrist problem, and he blazes a backhand down the line to show his opponent he isn't intending on conceding defeat. That said, the errors are continuing to come and Federer earns a break point, effectively a match point. Nishikori saves it, and a second break point, but he double faults on a third to leave Federer requiring just one more service hold for victory.

MATCH! There's still life left in Nishikori though! The Japanese produces two of his best points of the match to get to 0-30 but Federer finds a timely first serve to halve the deficit. Nishikori follows that with a return that just misses the line and Federer is two points away. However, the Swiss misfires with a backhand and Nishikori has a break point! It's saved by Federer though, who then moves to match point with a backhand winner. A big serve is all he needs to secure victory and effectively take him through to the last four.

The scoreline is harsh from a Nishikori perspective, but that was mightily impressive from Federer. He was fully aware of the threat that the US Open runner-up posed but he took away his weapons in style. He will be guaranteed of his place in the semi-finals if Milos Raonic defeats Andy Murray later this evening.

That will be all from Sports Mole's coverage of this match but we hope that you return for Murray's hugely important match with Raonic later today. Goodbye for now.