NEW YORK -- Roger Federer served poorly. He volleyed poorly. He closed out sets poorly, too. And now he's gone, beaten at the US Open by an opponent ranked outside the top 50 for the first time in his illustrious career.
Looking slow and tired on a sweltering night in Arthur Ashe Stadium, the No. 2-seeded Federer double-faulted 10 times, failed to convert a trio of set points and lost 3-6, 7-5, 7-6 (7), 7-6 (3) in the fourth round to John Millman in a match that began Monday and concluded at nearly 1 a.m. Tuesday.
To Federer, it was all about the heat and the humidity. With the temperature in the 80s, even with the sun down, and the humidity at about 75 percent, he was unable to summon his usual verve.
"Was just one of those nights where, I guess, I felt I couldn't get air. There was no circulation at all. I don't know, for some reason I just struggled in the conditions tonight. It's one of the first times it's happened to me," Federer, 37, said. "It's uncomfortable. Clearly just keep on sweating more and more and more and more as the match goes on. You lose energy as it goes by. But John was able to deal with it better."
It's only the second time in Federer's past 14 appearances at the US Open that he has lost before the quarterfinals. He is, after all, a five-time champion at the tournament, part of his men's record haul of 20 Grand Slam titles.
"In all honesty, Roger's a hero of mine. I look up to him,'' said Millman, an Australian who is 29. "I felt a little bit guilty today, because he didn't have his best day, and that's for sure. I know that. I'm very aware he didn't have a great day in the office. Probably, to beat him, I needed him to have an off-day and I needed to have a decent, good day."
So much for that highly anticipated matchup between Federer and 13-time major champion Novak Djokovic in the quarterfinals. Instead, it'll be the 55th-ranked Millman, who had never made it past the third round at a Slam until last week, taking on No. 6 seed Djokovic.
Hours before, Djokovic left the court for a medical timeout -- the second time during the tournament he has sought help from a doctor because of harsh conditions -- during what would become an otherwise straightforward 6-3, 6-4, 6-3 victory over 68th-ranked Joao Sousa of Portugal.
"I'm not 21 anymore. That was 10 years ago. I still don't feel old. But at the same time, there is a little biological clock that is not really working in your favor," Djokovic said. "Sometimes, you just have to survive."
He reached the quarterfinals for an 11th consecutive appearance in New York as he bids for a third US Open championship and 14th Grand Slam trophy.
He improved to 28-0 at the US Open against opponents ranked outside the top 50, and here's another reason it wasn't all that surprising the way things went against Sousa: Djokovic is now 5-0 in their head-to-head series, taking all 14 sets they've played against each other.
The heat, though, is much tougher on Djokovic, who showed the same blank expression, rosy cheeks and sweat-soaked shirt as during his first-round match last week. That was the first time in tournament history that the US Open created an extreme heat policy for men's matches -- players can opt for a 10-minute break between the third and fourth sets -- similar to what's standard on the women's tour, in which there can be a delay between the second and third sets.
"It's not easy," Djokovic said, "to play in these kind of conditions."
The other quarterfinal in the bottom half of the draw will be a rematch of the 2014 US Open final: No. 7 Marin Cilic against No. 21 Kei Nishikori.
Cilic, who beat Nishikori four years ago for his only major title, was a 7-6 (6), 6-2, 6-4 winner against No. 10 David Goffin, while Nishikori advanced by defeating Philipp Kohlschreiber 6-3, 6-2, 7-5.
"He pushed me around," Kohlschreiber said after Nishikori reached the final eight for a second straight Grand Slam tournament.
Both Nishikori and Djokovic missed last year's US Open with arm injuries.
"I don't have any pressure," said Nishikori, who was so crushed about missing the US Open last year that he couldn't even watch the tournament. "But [I'm] enjoying playing every match and enjoying playing tennis again a little more than before."
Millman was adamant he would not be intimidated by Federer, and perhaps was helped by having spent time practicing together a few months ago ahead of the grass-court portion of this season.
"I love his intensity," Federer said.
Still, this was a stunner. Not simply because Federer lost -- he entered the day 28-0 at the US Open, and 127-1 in all Grand Slam matches, against foes below No. 50 in the ATP rankings -- but how he lost. Start with this: Federer held two set points while serving for the second at 5-4, 40-15 and did not pull through. Millman knew that was the turning point.
"At the start, I don't think I was playing so well," said Millman, who noted he was sweating so much he had a hard time holding on to his racket. "But, yeah, as the match went on, I felt more comfortable, felt pretty good.''
Then Federer had a set point in the third at 6-5 in the tiebreaker, but again was stymied.
In the fourth set, he went up a break at 4-2, yelling "Come on!" and getting all of those rowdy spectators in their "RF" gear on their feet, prompting the chair umpire to repeatedly plead for silence. But Federer uncharacteristically got broken right back with a sloppy game, most egregiously when he slapped what should have been an easy putaway into the net.
And then there was his serve. He put only 49 percent of his first serves in play, including a hard-to-believe 31 percent in the second set. This is a guy whose combination of precision and power on that stroke is considered as good as anyone's ever.
In the final tiebreaker, he double-faulted twice in a row.
The first obvious signs of trouble for Federer came far earlier, in the second game of the second set. He started that 15-minute struggle by missing 18 of his initial 20 first serves. While he eventually held there, he needed to save seven break points along the way. It was clear Federer was not at his best.
Millman's big rips on groundstrokes didn't help matters. Nor did his steeliness despite not being all that familiar with this sort of success or setting. This is a guy who had never managed to beat a top-10 player, let alone a man who has spent more weeks at No. 1 in the ATP rankings than anyone else.
As the unforced errors mounted -- Federer would finish with 76, compared to Millman's 28 -- Federer's wife, Mirka, couldn't bear to look, putting her head in her hands in the guest box in the stands.
Federer hung his head at a changeover, a little fan pointed right at his face, but nothing seemed to make him feel like himself.
"When you feel like that," Federer said, "everything is off."
The Associated Press contributed to this report.