US Open: Kei Nishikori Ran Out of Gas vs Stan Wawrinka

Kei Nishikori did the hard work by knocking world number two Andy Murray out of the US Open but blunting the free swinging backhand of Stan Wawrinka was a step too far.

The Japanese star took the first set off the third-seeded Swiss but in Friday's crushing humidity and heat, he simply ran out of gas in the semi-final, losing 4-6, 7-5, 6-4, 6-2.

"I went a little too much to his backhand. He started using the backhand down the line. He can hit angles really well with topspin. Yeah, definitely I was struggling with his backhand," said the 26-year-old.

Nishikori had reached the final in New York in 2014 where he lost to Marin Cilic. After enjoying a five-set win over Wimbledon champion Murray in the fourth round, he was tipped to return to the final this year.

But the efforts of beating Murray proved too much.

"It's not easy when you have to play No. 2, No. 3, and, you know, Novak Djokovic was waiting in the finals," said Nishikori.

"It wasn't easy but if I could have won the last few matches a little easier I could have had more chance today and maybe reach the final."

Despite the loss, Nishikori said "it was a good summer" after finishing runner-up at the Toronto Masters and winning a bronze medal at the Olympics.