Both players struggled in an error-strewn encounter with high temperatures in New York again a factor.

Cilic made a dominant start to lead by a set and a break before his level dropped to allow Japan's 21st seed Nishikori to take a 2-1 lead.

Cilic recovered to force a decider but Nishikori edged through 2-6 6-4 7-6 (7-5) 4-6 6-4 in four hours eight minutes.

The 28-year-old will play Novak Djokovic, who beat Australian John Millman, in the last four.

After Naomi Osaka reached the women's semi-finals earlier, Nishikori's win means there is a Japanese man and woman in the last four of a Grand Slam for the first time in the Open Era.

"It's great to see," Nishikori said.

"I hope people were watching us. Hopefully many people were cheering in support.

"Naomi's doing well, because she has won a Masters (Indian Wells). I think she can win a title now. It's a big chance for her."

Errors dominate in New York heat

There was a subdued atmosphere on Arthur Ashe Stadium with the crowd struggling to get into the match which was a repeat of the 2014 US Open final won by Cilic.

Both players hit comfortably more unforced errors than winners with Cilic making 70 unforced errors to 57 winners and Nishikori 45 to 29.

The momentum swung throughout the match with Cilic looking in control when leading 4-2 in the second set before losing six games in a row.

He also lead with a break in the third-set tie-break before hitting two consecutive double faults to gift Nishikori the advantage.

Even in the final set Nishikori looked comfortable with a 4-1 lead before Cilic levelled, only for the Croat to lose the final two games.

"I came back, I had some chances," said Cilic. "With a great quality player like Kei, he also had his chances, and he converted. So it came down to a couple points."