Image source, AFP

The clock ticks beyond midnight in Blighty. This match is approaching its fourth hour. The Nishikori forehand on song, helping him level the score at 30-30, but big serving from Wawrinka takes him over the line. The Swiss muttering to himself in between points, trying to ease the nerves.

Update from the juniors - and it is good news for British duo Freya Christie and Katie Swan who have knocked out second seeds Anhelina Kalinina (Ukr) and Iryna Shymanovich (Blr) 7-6 (10-8) 6-4 to make it into the third round.

Nishikori's radar faltering slightly, screwing a forehand wide to give Wawrinka a sniff at 15-30. An attempted backhand crosscourt into the tape and Wawrinka has two break points.

Will the third seed turn the screw? Brilliant from Nishikori as he holds firm and turns defence into attack with two thunderous forehands. One saved. It's that forehand to the rescue again. Boom. Two break points saved. Deuce.

A little drama as the next point is replayed, a late call from Nishikori much to Wawrinka's annoyance. The wild-eyed Swiss rubbing his jaw, muttering. His chance has gone. A cute volley from Nishikori and the 10th seed lives on.

Crisp serving from the Swiss - an ace down the 'T' eases him to 40-0. The Australian Open champion gives his opponent little chance, working him to his forehand side and Nishikori nets.

A wild forehand from Nishikori allows Wawrinka to level at 15-15, but the 10th seed reverts to serve and volley and the ploy works. He wraps up the game with a forehand winner and there's no sign of the man from Japan wilting just yet.

BBC Radio 5 live sports extra

John Morris, who represents Nick Kyrigos: "It was a huge effort from Stan Wawrinka to get through that fourth set. With Nishikori clearly struggling, I can't see him getting over the line now, which is a shame."

Image source, AP

So who thought it would be that simple? Nope.

Nishikori was two shots away from a place in the semi-final, but Wawrinka then wins the next point for set point - and he is serving.

Nishikori's return goes long. Ladies and gentleman, boys and girls, we have a fifth set.

Hutchins and Chan have thrown away a large lead in the first set of their mixed doubles semi-final, and Wawrinka is in danger of losing a similar good position in this tie-break. He was 4-0 ahead, now it is 5-5. Nishikori two points away from the match.

Piers Newbery
BBC Sport at Flushing Meadows

Image source, Getty Images

"They were 5-0 up after 15 minutes, they are now 7-5 down after 42 minutes. And just to rub salt in the wound, Hutchins and Chan led 0-40 in the final game. That could be a tough set to recover from."

We are on course for five sets. Wawrinka is 4-0 up in the tie-break. Three hours, 26 minutes and counting so far for this match.

Image source, EPA

How will Nishikori's fitness hold up? What a test for him. Can he come through it? We will see, so stay with us. Sleep is overrated anyway.

Nishikori holds the 12th game to love. And for the second successive set we have a tie-break situation. Can Nishikori take it to move into his first Grand Slam semi-final?

Piers Newbery
BBC Sport at Flushing Meadows

"Hutchins and Chan have a bit of a shocker after racing into a 5-0 lead. Two double faults in a row see Hutchins broken in game nine and Mirza levels it up on serve at 5-5. The best guess is we're up to around 200 spectators now."

Ross Hutchins and Yung-Jan Chan are playing Sania Mirza and Bruno Soares, the top seeds, in the semi-finals of the mixed doubles.

Wawrinka takes the 11th game of the fourth set to love. We're all starting to look at which of the tables at the BBC offices we will be sleeping on later.

For those waiting for Andy Murray, and let's face it, that's probably most of us, we still have Serena Williams to play first after the conclusion of the Wawrinka v Nishikori match.

But, on the flip side, this is a great encounter between these two players.

Five-five. Fourth set. Two sets to one to Nishikori.

BBC Radio 5 live sports extra

John Morris, who represents Nick Kyrgios: "That was probably Stan's best bit of tennis for half an hour. He was very aggressive, coming into the net and Nishikori, whether it was through fatigue or weight of shot, was opening his racquet face."

Image source, Getty Images

A missed volley from Nishikori at 40-15 down gives Wawrinka a 5-4 lead. Nishikori, who edged out fifth seed Milos Raonic of Canada in a five-set thriller on Tuesday, is now serving to stay in the fourth set. One more break for Wawrinka and it will be a second consecutive five-setter for the Japanese.

The players are rattling through the games and there is no more showboating from Nishikori. It is all business now as he pulls it back to 4-4.

Rachael Collins:, external Wishing Wawrinka v Nishikori was on the telly - it's sounding like a thrilling match from live text coverage #bbctennis.

Katie O:, external Tried to have a nap but not sleepy yet. Coffee for me... #bbctennis

John McEnerney:, external It will be some story if Nishikori beats Stan, test of both their metal! Can KN close it out or can SW fight back & win?

Right, this game is moving into the critical phase. Wawrinka maintains the pressure by taking the seventh game of the fourth set, but the world number four, seeded third in the absence of Rafael Nadal, trails by two sets to one.

Andy Murray spotted on the practice courts - with coach Amelie Mauresmo overseeing the session.

Looks like he'll have plenty of time to warm up with the way this Wawrinka vs Nishikori match is going.

If the British number one finds a spare minute or two in his lengthy preparation, perhaps he'd care to read this article about how he can beat Novak Djokovic - according to the stats.

Some British fans are in. They may not have been overly excited when they found out Murray was playing in the second, not first, session of the day.

Image source, AP