Roger Federer said he was "happy the match was over" after playing in "uncomfortable" conditions during his shock fourth round US Open defeat.
The 37-year-old Swiss - a five-time champion at Flushing Meadows - was beaten 3-6 7-5 7-6 (9-7) 7-6 (7-3) by world number 55 John Millman.
Their match finished just before 01:00 local time but temperatures still hit 30C with high humidity levels.
"I felt I couldn't get air. There was no circulation at all," Federer said.
"It's uncomfortable. Clearly you just keep on sweating more and more and more and more as the match goes on.