Slight delay as Nishikori leaves the court. He re-emerges, shaking out his right wrist slightly.

A close-up of Nishikori during the last game showed him grimace and after a shot. He received medical treatment on the same issue last time out. Could that start to become a problem as this game enters a deciding set?

Image source, AFP

Nishikori lands a pair of big serves then hoists a pinpoint lob over his opponent to open up two set points. A clean backhand winner ensures we are going to a deciding set for the first time in the tournament.

Miles Maclagan
Former coach to Andy Murray and Laura Robson on BBC Radio 5 live sports extra

Image source, EPA

"If it does go to a third set, Nishikori's record this year is something like 15 wins to two losses. Ferrer is extremely fit and you'd think if it got down to the third set he'd be able to match him - but so far between these two this year, Nishikori has beaten him every time."

Ferrer attacks the net and pulls of a crisp backhand volley to go 40-15 up. Another big serve gets him the game. This is high quality tennis from both players, with very few unforced errors.

Tim Henman
Former British number one on BBC Two

"There's this debate going about whether these championships move on from London when the current contract ends. I hope not. They get incredible crowds here and it is a fantastic season-ending tournament."

Ferrer plays one of his best shots of the match to pass Nishikori at the net, but it proves to be his only point of the game as the Japanese moves to within one game of the set.

Andrew Castle
BBC tennis commentator on BBC Two

"We're starting to talk about a third set here. We haven't seen a deciding set in the whole tournament so far - no match has gone to the best of three - amazing."

Just like his opponent, the 32-year-old Ferrer seems to be finding his service rhythm when it matters.. He recovers from 15-30 when Nishokori mis-times a couple of groundstrokes.

Image source, Getty Images

Nishikori is landing a lot more first serves now. His second set percentage is over 70, whereas he was in the low 50s in the first set. Two big serves finish off a service hold to 15.

Nishikori takes a forehand early for a winner to earn a deuce on the Ferrer serve. The Spaniard holds on to keep in touch in this second set.

Ferrer finds the sweet spot to lace a backhand down the line and put pressure on the Nishikori serve at 15-30. The Japanese keeps his cool and keep his break of serve intact.

It's a big "if" I know, but if these two had big serves they'd be right up there with the likes of Federer and Nadal. I hesitate to write Djokovic too, because having watched him last night, I'm convinced he's is on another planet right now.

Image source, Getty Images

Ferrer is using the whole court to put Nishikori through his paces. Another love game is completed when the Japanese goes long.

Nishikori shows his feathery touch once again to land the perfect drop shot and holds serve to love. Good start to the second set for the world number five.

Ferrer takes his eye off the ball and is soon three break points down. Two are saved, but Nishikori snaffles the third to seize the early running in the second set.

Piers Newbery
BBC Sport at the O2 Arena in London

"Cries of "Vamos!" have been in unusually short supply at the O2 this week in the absence of Nadal and, until now, Ferrer but Spanish voices can be heard now as their man takes control. There might be a few Swiss whoops around too as that set means Federer is through to the semis. I think."

Oh dear, looks like we put the mockers on Nishikori. He plays a howler of a game to lose the first set. He misses a chance to challenge that would have won his a point, then double fault to go 15-40 down. A smash into the net gives Ferrer the set.

Chris White, you may have a point. He certainly has great grace around the court. But he'll have to take one of those hands off his backhand to get anywhere near Federer's beauty to me.

Here he is, serving to stay in the set.

Tim Henman
Former British number one on BBC Two

Image source, Reuters

"Ferrer doesn't play the board, just the ball. What I mean by that is that you'd never know whether he's a break up or a break down. He doesn't ever get despondent, he's just relentless. This is him day in, day out - whether on the practice court or match court, he fights for every ball."

Chris White:, external Dare I say it? Nishikori the most beautiful player since Federer?