Kei Nishikori overcame seventh seed Marin Cilic in a gruelling five-set match to reach the US Open semi-finals.
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 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.
He will play either Serbia's Novak Djokovic or Australian John Millman in the last four.