Alexei Popyrin stuns the world No 2, who will end the season without a Grand Slam title for the first time since 2017.

Defending champion Novak Djokovic suffered a major upset at the US Open, losing to Alexei Popyrin, who ended the Serbian’s bid for a record-breaking 25th Grand Slam title.

Australian Popyrin defeated Djokovic 6-4, 6-4, 2-6, 6-4 in the third round at Flushing Meadows on Friday.

“I spent a lot of energy winning the gold, and I did arrive to New York just not feeling fresh mentally and physically,” Djokovic told reporters. He won the gold medal in the men’s singles at the Paris Olympics earlier this month.

Popyrin, who lost to Djokovic at both the Australian Open and Wimbledon this year, raised his arms in triumph as he reached the round of 16 of a major for the first time.

“Third time lucky I guess,” Popyrin said in an on-court interview.

Djokovic, 37, was uncharacteristically sloppy, with 14 double faults – a record for him in a Grand Slam match – while his 25-year-old opponent smacked 50 winners.

The world No 2 had five break point chances in the opener but failed to convert any of them, while Popyrin broke serve on his first opportunity for a 5-4 lead and won the first set.

Popyrin broke again in the second when Djokovic’s volley landed wide for a 3-2 advantage and took control of the match with a perfectly executed serve and volley to take the second set.

Djokovic showed some life in the third, but the comeback was shortlived as Popyrin crushed a ferocious forehand winner for a break of serve and 3-2 lead in the fourth.

“I have played some of the worst tennis I have ever played, honestly,” Djokovic said. “Serving – by far – the worst ever.”

His defeat followed the shocking exit of the 2022 champion, Carlos Alcaraz.

Alcaraz entered the US Open as the tournament favourite having won the French Open and Wimbledon, but was eliminated by 74th-ranked Botic van de Zandschulp 6-1, 7-5, 6-4 on Thursday.

It’s only the third time in the Open era that two of the top three men’s seeds at the US Open crash out before the fourth round, the other such instances in 1973 and 2000.

“It was just an awful match for me,” Djokovic said. “I wasn’t playing even close to my best. It’s not good to be in that kind of state where you feel OK physically, and of course you’re motivated because it’s a Grand Slam, but you just are not able to find your game.

“That’s it. The game is falling apart, and I guess you have to accept that tournaments like this happen.”

Djokovic was attempting to become the first player in tennis history with 25 Grand Slam singles titles. Instead, after knee surgery in June, he finishes a year without claiming at least one major championship for the first time since 2017.

Djokovic has reached the US Open final 10 times, and won in 2011, 2015, 2018 and 2023.

Popyrin will now try to reach his first Grand Slam quarterfinal by getting past Frances Tiafoe, who advanced on Friday with a 4-6, 7-5, 6-7 (5), 6-4, 6-3 win over Ben Shelton in a matchup between two Americans.

“If he serves well, plays well, he can beat anybody,” Djokovic said about Popyrin. “Look, Alcaraz is out. I’m out. Some big upsets. The draw is opening up.”