(CNN)Five-time champion Roger Federer crashed out of the 2018 US Open in a stunning fourth-round loss to Australian John Millman.
The Swiss, who last won the tournament in 2008, went down 3-6 7-5 7-6 (9-7) 7-6 (7-3) to the world No. 55 in three hours and 34 minutes.
The out-of-sorts Federer failed to convert set points in the second and third sets before faltering again in the fourth.
Two Federer double faults put his opponent 4-1 up in the tie-break and an overcooked Federer forehand secured a memorable win for the 29-year-old Millman, who will next play Wimbledon champion Novak Djokovic in the quarterfinals.
It is the first time Federer, who has only failed to reach the quarterfinals of a grand slam on seven occasions, has lost to a player ranked outside the top 50 at the US Open.
"It was very hot, one of those nights where I felt I couldn't get air," Federer, who made 77 unforced errors in the match, told reporters.
"There was no circulation at all. For some reason, I struggled in the conditions. It's one of the first times it's happened to me. I do believe since the roof is on that there is no air circulation in the stadium. That makes it a totally different US Open.
"But John was able to deal with it better. He comes from maybe one of the most humid places on earth, Brisbane. I knew I was in for a tough one. I was just happy that the match was over."