Roger Federer was beat in the fourth round of the US Open in New York.
The five-time champion at Flushing Meadows was defeated 3-6 7-5 7-6 (9-7) 7-6 (7-3) by world number 55 John Millman.
Federer, 37, said: "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. You lose energy as it goes by.
"At some point also I was just happy that the match was over, I guess."
Millman - the only unseeded player left in the last eight of the men's draw - will play two-time champion Novak Djokovic in his first Grand Slam quarter-final on Wednesday.