Defending champion Novak Djokovic dumped out by Alexei Popyrin at US Open

One day after third seed Carlos Alcaraz slumped to a shock defeat against 74th-ranked Botic van de Zandschulp, Popyrin robbed the tournament of another superstar with a 6-4, 6-4, 2-6, 6-4 victory.

Popyrin handed Djokovic his earliest US Open exit in 18 years and his earliest Grand Slam exit since he fell in the second round of the Australian Open in 2017 - which was also the last year the Serbian great failed to claim a single Grand Slam title.

Although he won the Olympic gold he had long coveted at the Paris Games, an uneven season that included knee surgery saw Djokovic come up empty in the majors.

He had beaten Popyrin in three prior encounters, including at the Australian Open and Wimbledon this year, but 14 double faults - and 49 unforced errors total - were too much for Djokovic to overcome.

"It was just an awful match for me," Djokovic said, adding that he would now try to "recalibrate and look forward".

Popyrin, coming off the biggest title of his career at the Montreal Masters, seized the first two sets with a fearless display on serve and from the baseline.

Djokovic gave himself some breathing room with an early break in the third. Popyrin clawed back the break only for Djokovic to break him twice more, the Serbian taking full advantage of Popyrin's mounting errors.

But the Aussie responded in a tense fourth set, saving break points in the second game before seizing a break for a 3-2 lead.

He stayed patient as Djokovic saved three break points and when the Serbian double faulted to gift him another Popyrin capitalized with a blistering forehand winner and let out a massive roar.

After saving a pair of break points in the next game, the Aussie broke again for a 5-2 lead.

Djokovic, not about to go quietly, won two straight games to cut the gap but Popyrin claimed the match with a love game as Djokovic fired one more forehand long.

"We had some battles at the Australian Open and Wimbledon," Popyrin said. "This match was a little different. I was able to take my chances when I had them.

"To be in the fourth round of a Grand Slam by beating the greatest of all time is unbelievable," Popyrin said.