Andy Murray knocked out of US Open by Kei Nishikori

Both players saw their form hit peaks and troughs at almost minute-by-minute intervals as the scoreline ended up with Nishikori winning 1-6 6-4 4-6 6-1 7-5, the Japanese twice fighting back after falling a set behind in the match.

"Actually it was too exciting on court," said Nishikori.

"There were many ups and downs, in the beginning I didn't play well."

But Nishikori admitted that a rain delay in the second set aided him.

"It helped me a lot," he said. "I needed to re-think my tactics."

The Scot started the match as a hot favourite to make it through, having been in blistering form in his quarter-final match, and whistled through the first set 6-1 in just over half an hour.

Murray looked in charge of the second set as he went a break up, but the rain delay changed the momentum in the match - and Nishikori broke back, before breaking again with Murray serving at 4-5 down in the second.

That levelled the match - and the Scot, so dominant early on, now knew exactly what faced him: this was the Nishikori who had beaten the world number two before and who is a former US Open finalist, having knocked out Novak Djokovic on this very same Arthur Ashe Court in the semi-finals in 2014.

Murray got back in front by winning a close-fought, topsy-turvy third set that saw five breaks of serve - including three in a row at the end of the set.

But it all changed around again within minutes. Nishikori utterly dominated the fourth set, sparked from the moment Murray lost the plot when the umpire ruled him to have lost a point when Murray expected a let to be played following a loud noise emanating from the roof.

Murray was totally unsettled, railing at the umpire after the game, clearly furious at what had happened.

Nishikori went along with his business quietly and efficiently as Murray was losing the plot, the underdog winning five games in a row to turn 1-1 into 6-1 and set the match up for a decider.

Murray was then broken in the opening game of the final set, and though he broke back quickly he immediately lost his own serve again to cede the advantage to his opponent once more.

With the finish line in sight, however, Nishikori faltered: serving at 4-3, he got to 40-0 up but a succession of unforced errors saw him blow five points in a row to lose his service and put the match on a knife-edge once more.

Both men then held serve, Murray digging deep to do so while Nishikori managed it without losing a point - giving Murray the chance to serve for a 6-5 lead and guarantee himself at least a tie-breaker.

Once again, however, Nishikori broke serve with an incredible succession of shots - charging the net at times, other times hitting fine winners from beyond the baseline.

And he then held serve once more to complete an incredible match, and one of the finest victories of his career.

"I have great memories here. Two years ago I made the final and I'm really happy to make the semi-final again," said Nishikori, who lost to Marin Cilic in the 2014 final.

"An easy day tomorrow and then let's focus on the next one."