So we already know that Denmark's Caroline Wozniacki will meet unseeded Shuai Peng of China in one semi-final and that Russia's Ekaterina Makarova will be one of the players in the other semi-final.

Image source, Reuters

Who will she meet? Five-time US Open winner Serena Williams will start as the favourite, as she does in most of her matches, and she faces Italy's Flavia Pennetta (pictured).

That match is coming up shortly, and after that it will be the Andy Murray v Novak Djokovic tie in the last of the men's singles quarter-finals.

BBC tennis correspondent Russell Fuller:, external Welcome to the Grand Slam semi-final club Kei Nishikori: fantastic fight to see off Stan Wawrinka in five sets. Rarely took a step backwards. It took Nishikori four hours, 15 minutes - four minutes fewer than he needed to beat Milos Raonic at 2.26am yesterday morning.

Image source, AFP

BBC Radio 5 live sports extra commentator David Law:, external Nishikori was as uplifting as Wawrinka at the Australian Open. Fearless, fantastic tennis.

American journalist Ben Rothenberg, external and BBC Radio 5 live sports extra analyst: Unless Novak Djokovic wins the #USOpen, the four Grand Slam titles in 2014 will have been won by four different men + four different women.

Angel Di Maria:, external Well played Nishikori. Incredible stamina and courage. Brilliant.

Obviously, that is not the REAL Angel Di Maria, although if the real one wants to contact us then he is more than welcome.

The real one has been busy himself tonight by setting up three goals and scoring once in Argentina's 4-2 win against Germany. In other football news, England beat Norway 1-0 thanks to Wayne Rooney's penalty.

Piers Newbery
BBC Sport at Flushing Meadows

"It was not to be, Ross Hutchins misses out on a first Grand Slam final after he and Taiwan's Yung-Jan Chan lose 7-5 4-6 10-7 to Sania Mirza and Bruno Soares, as the cheers from Nishikori's win on Ashe drift across the grounds."

Image source, Getty Images

Kei Nishikori after becoming the first Japanese player to reach a Grand Slam semi-final in the Open era: "I started a little bit tight but my body was OK. As the game was going on, I got more confidence. I don't know how I finished the game but I'm very happy."

BBC Radio 5 live sports extra

John Morris, who represents Nick Kyrigos: "Unbelievable effort from start to finish. He came out very tired looking and for him to outlast Wawrinka in over four hours after what he went through the other night is monumental.

Wawrinka saved the first match point, but Nishikori wins it at the second attempt. What an effort from Nishikori, who becomes the first player from Japan to reach a Grand Slam semi-final in the Open era.

He beat fifth seed Milos Raonic in the last round, and has now knocked out the third seed as well.

Match point for Nishikori.

Image source, Reuters

A lovely drop shot from Nishikori helps him hold his serve to love. He has battled a toe injury, and was involved in a five-set thriller in the last round. He needs one more game to move into the semi-final.

Piers Newbery
BBC Sport at Flushing Meadows

"Things are looking up on Armstrong from a Brit/Taiwanese perspective, with Hutchins and Chan taking the second set despite letting another lead slip. With the sun dipping behind the stands, the floodlights are required as we head into a Champions' Tie-Break - first to 10."

It is now 4-4. Who is going to blink first?

Levi Crisp:, external Can't even nap when Nishikori v Wawrinka is this good. Hope I don't wake up any other students living all round me during Murray #bbctennis

Michael Chang is a bit happier now as his man holds his serve, although Wawrinka had won two points to make it a nervy occasion.

Whatever the result, this has been a fantastic attempt from Kei Nishikori, coming less than two days after he was involved in a five-set thriller against Milos Raonic.

We have now been playing for four hours. Who will be the last man standing? Nishikori's coach, Michael Chang, a US Open finalist back in 1996, looks a worried man.

Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra

"To have two five-set matches in a row really takes its toll and Nishikori's face is red and he looks like he has been in a boxing match."

Wawrinka wins the sixth game to love after Nishikora powers the last shot into the net. 3-3 in the fifth set. Fine serving from the Swiss. Can Nishikori claim a surprise victory here?

Just a reminder that our next match will feature Serena Williams as the American takes on Italy's Flavia Pennetta later on in their women's singles quarter-final tie.

If Wawrinka were walking along your high street talking to himself as he is on Ashe, you'd calmly, but quickly, move in the opposite direction. The Swiss pumped up and oblivious to those around him. But he wastes a break point - his backhand return floating into the tramlines.

Wawrinka perhaps needs to be more aggressive from the baseline. Nishikori comes out on top of a tussle from the back of the court, and seals the deal as Wawrinka's backhand bounces long.