2024 US Open - Day 3
NEW YORK, NEW YORK - AUGUST 28: Novak Djokovic of Serbia returns a shot against Laslo Djere of Serbia during their Men's Singles Second Round match on Day Three of the 2024 US Open at USTA Billie Jean King National Tennis Center on August 28, 2024 in the Flushing neighborhood of the Queens borough of New York City. Photo by Al Bello/Getty Images

Novak Djokovic, the defending US Open champion, has been knocked out of the tournament by Australian Alexei Popyrin in a stunning third-round upset. Popyrin, seeded 28th, defeated Djokovic 6-4 , 6-4, 2-6, 6-4 to reach the fourth round of the Grand Slam tournament.

Djokovic, 37, was seeking to win his 25th Grand Slam title, but Popyrin's impressive performance ended his bid. The Serbian tennis star was error-prone throughout the match, committing 15 double faults and hitting 50 winners.

"It's unbelievable," Popyrin said after the match. "I've been to the third round about 15 times in my career, but I haven't been able to get to the fourth. To be able to do it against the greatest of all time... it's a great feeling."

Djokovic's Worst Ever

Djokovic, who has been struggling with his form this season, admitted that he played some of the worst tennis of his career. "I played some of the worst tennis I have ever played," he said, according to Independent. "Serving by far the worst ever. If you play on a quick surface like this without the serve, without ability to win free points there, many double faults, then you can't win."

The defeat means that Djokovic will go through a season without a Grand Slam title for the first time since 2017. He remains tied with Margaret Court for the most Grand Slam titles in history, with 24.

The upset has opened up the bottom half of the draw, with American players Frances Tiafoe, Taylor Fritz, and Brandon Nakashima now having a chance to reach the final.