Ross Hutchins and Yung-Jan Chan have made an excellent start in their mixed doubles semi-final. The pair are 4-0 up in the first set against top seeds Sania Mirza and Bruno Soares.

A double fault from Nishikori leaves it at 30-30 on his serve. But a powerful forehand then takes the Japanese to game point, before Wawrinka takes it to deuce.

Image source, Getty Images

The Swiss then has a break point but can only clip the top of the net with his shot. With that, we have now been playing for three hours. So who is staying awake then for the whole night? Does it really matter if you're a bit tired tomorrow?

By the way, Nishikori then takes the game. A mini-opportunity for Wawrinka evaporates.

Little excitement so far in the fourth set and it is all quite routine. Wawrinka is untroubled and moves into a 3-2 advantage.

Despite the treatment on his toe, Nishikori then holds his serve for 2-2.

Piers Newbery
BBC Sport at Flushing Meadows

"After fighting through the multitudes at the Food Court, a brave handful have made it to Armstrong to see if Ross Hutchins can make his first Grand Slam semi-final, alongside Taiwanese partner Yung-Jan Chan. The theme from 'Fame' blasts around the empty arena, weirdly."

Image source, AP

Brit Hutchins and Yung-Jan Chan face the top seeded pair of Sania Mirza (India) and Bruno Soares (Brazil) in the semi-finals of the mixed doubles.

After Nishikori makes it 1-1 in the fourth set, Wawrinka takes the next for a 2-1 advantage in the fourth set.

But hold on just a minute. Nishikori then has to call for medical attention. He has been suffering with a toe problem, and has some nasty blisters under a bandaged toe. He leads 2-1 in sets and is having to play through the pain barrier.

He does not look comfortable out there. The physio wraps his foot in a new bandage and Nishikori should be OK to carry on. He is aiming to become the first Japanese player to reach a Grand Slam semi-final in the Open era so will definitely not want to have to withdraw.

Stats fans rejoice.

So far, these are some of the figures.

First serves in: Wawrinka 52%, Nishikori 65%

Winners: Wawrinka 16, Nishikori 13

Unforced errors: Wawrinka 19, Nishikori 13.

Back on the court, Nishikori makes it 1-1.

Wawrinka takes the first game to love. He looks angry and like he means business in the fourth set.

Don't forget, the main event of the evening / night / early morning is the men's quarter-final between Andy Murray and Novak Djokovic.

This is how the pair have got on against each other.

The pair have met in four Grand Slam finals. Murray won the 2012 US Open and 2013 Wimbledon finals, with Djokovic taking the 2011 and 2013 Australian Open titles.

Their match at Flushing Meadows is scheduled to start no earlier than 02:00 BST on Thursday morning, but with this Wawrinka v Nishikori encounter turning into an epic, that time may well be pushed back a bit.

A quick round-up of the British juniors in action at Flushing Meadows:

Katie Swan (pictured below) lost to the ninth-seeded Ukranian Anhelina Kalinina 6-3 6-2 in round two of the junior girls' singles.

Image source, Getty Images

In the junior girls' doubles, 17-year-old Isabelle Wallace and her Romanian playing partner Ioana Loredana Rosca lost a match tie-break to go down 6-2 1-6 11-13 to fourth seeds Jelena Ostapenko (Lat) and Olga Fridman (Ukr) in round two.

But British compatriot Maia Lumsden did make it through to the third round of the junior girls' doubles with her playing partner Fanni Stollar (Hun). They upset Russian eighth seeds Anna Kalinskaya and Evgeniya Levashova 6-3 7-6 (7-4).

British duo Freya Christie and Swan will be hoping for similar success in their match later on court seven against second seeds Anhelina Kalinina (Ukr) and Iryna Shymanovich (Blr).

A thrilling set ends with Nishikori moving into a 2-1 lead. He lost the first set 6-3 but has fought back to take the next two 7-5, 7-6 (9-7). Great entertainment at Flushing Meadows.

Ever get the feeling this is going all the way? One set all, 5-5 in the tie-break.

The floodlights are on, even though we have bright sunshine at Flushing Meadows. Wawrinka has the advantage now at 5-3, after a 24-shot rally ends with Nishikori sending a cross-court shot wide.

Image source, Getty Images

A sensational backhand winner down the line from Wawrinka sees him recover after Nishikori had gained an early advantage in the tie-break. We are back with serve. Who will move two sets to one ahead?

Image source, AP

The purists may not be enjoying Nishikori's showboating, but the Flushing Meadows crowd are lapping it up. However, Wawrinka may not have the majority of the support from the neutrals, but has forced a tie-break in the third set.

Piers Newbery
BBC Sport at Flushing Meadows

"Nishikori's decision to go for a 'tweener' between-the-legs shot when serving for the set went down predictably badly with the wise and experienced heads watching from courtside - not exactly 'percentage tennis'.

"With 90 minutes until the night session is due to start, and at least 20 minutes usually needed to get the day crowd out and the later ticket holders in, we could be looking at a delay if this goes to five."

Nishikori has the whole court to aim at but sends his volley past the baseline. Are his recent efforts, that included a five-set match against Milos Raonic on Tuesday morning taking its toll?

Well, maybe not. Some more entertainment for the crowd sees Nishikori jump, spin and hit a winner (while facing the other way) that has Wawrinka applauding. Nishikori eventually holds and is 6-5 ahead in the third set, and one set apiece.

The crowd is getting larger as the match is progressing and they are being treated to some lovely tennis. A cute drop shot from Wawrinka has Nishikori on his toes, but does enough to just about get there in time andreturn it. The Swiss then forces a volley from Nishikori, who remained at the net, but the attempt is long.

It then becomes 5-5. You would be a brave person to bet on the winner of this one.

Nishikori the entertainer. A lob from Wawrinka sees the Japanese player galloping back and he attempts some showboating with the shot between his legs. but, although the crowd love it, it doesn't work and hits the top of the net.

Wawrinka then does the rest in the ninth game of the third set to break serve. This is looking like this is going to be a very long night.

Remember, Serena Williams is scheduled to start at midnight (British time), with Andy Murray v Novak Djokovic set to start at 02:00 BST. Anyone tired yet? Stay with us. You've come so far.