NEW YORK — There was no reason to believe that Roger Federer would have any trouble with John Millman in their fourth-round U.S. Open match in Arthur Ashe Stadium on Monday.

Millman was in the fourth round of a Grand Slam event for the first time. Federer had won 20 Grand Slam titles.

Federer was 40-0 at the U.S. Open against players ranked outside the top 50. Millman was ranked 55th.

Millman was 0-10 in his career against top-10 players. Federer was ranked No. 2.

And Federer, a five-time U.S. Open champion, had lost before the quarterfinals only once at the Open in the past 14 years.

Several hours earlier, Novak Djokovic had won his fourth-round match and in the minutes after his victory, he was already being asked about a possible quarterfinal matchup against Federer.

But it will be Millman facing Djokovic in the quarterfinals after a 3-6, 7-5, 7-6 (7), 7-6 (3) victory. The match ended shortly before 1 a.m. Tuesday.

“He’s been a hero of mine,” Millman said. “Today he was definitely not at his best, but I’ll take it.”

Federer had 10 double faults and got only 49 percent of his first serves in. He had 76 unforced errors.

It all added up to his earliest loss in a major tournament since a third-round loss at the 2015 Australian Open.

Federer has not won the U.S. Open since 2008, the last in a run of five straight Open titles.