World number one and defending US Open champion Novak Djokovic has been booed off the court after being forced to retire at the start of the third set of his fourth round clash with Stan Wawrinka on Arthur Ashe Stadium.
Djokovic had been dealing with a shoulder complaint all week and received treatment again during the round of 16 showdown.
But after dropping the first two sets and going down a break early in the third, Djokovic packed it in, retiring from the match at 6-4 7-5 2-1.
Djokovic, who has already won the Australian Open and Wimbledon titles this year, embraced Wawrinka on court and explained his decision before packing his bag and walking off.
He was followed off court and up the tunnel by a chorus of boos from the crowd.
After retiring against Stan Wawrinka Novak Djokovic is booed by tennis fans in New York at Arthur Ashe Stadium. Harsh. #USOpen pic.twitter.com/kakrRWm2Q7
— Omar Moore (@thepopcornreel) September 2, 2019
The booing divided opinion on social media, with many hitting out at the Flushing Meadows faithful.
Shameful that the crowd booed Djokovic. He's one of the greatest of all time and would never has withdrawn unless he was in severe pain.
— Still Bruce (@brucestill1) September 2, 2019
ya'll imagine being in immense pain while playing and getting booed. what kind of people are you? djokovic would've fought for that game if only he felt better. #USOpen #Djokovic
— M A Y O (@mayopararu) September 2, 2019
Say what you want about him but Novak Djokovic is one of the most professional athletes in our sport. He did not deserve to be booed for retiring & it has been well-documented that he has struggled with injuries this week, even if he has been pretty tight-lipped about it. #USOpen
— Max Gao (@MaxJGao) September 2, 2019
First Andrew Luck, and now Djokovic. I don't understand why a great player is booed for retiring because of an injury. The US Open has lost all class over the past couple of years. Waaaay too eager to denounce the situation (including last year's women's final).
— Sam Cam Entertainment (@SamCamEnt1) September 2, 2019
But for others, Djokovic's retirement was just the latest in a long list of instances that have seen the Serbian pull out.
Djokovic, a three-time US Open champion, has now withdrawn from 13 tournaments, including six Grand Slams.
His withdrawal against Wawrinka means he has now retired from every Grand Slam on the calender, including the 2005 and 2006 French Open, Wimbledon in 2007 and 2017 and the 2009 Australian Open.
In comparison, Roger Federer has never retired from a match.
Speaking after the match, Wawrinka said he felt for Djokovic.
"It's never the way you want to finish a match," Wawrinka said.
"I feel really sorry for Novak, he's a good friend, an amazing champion and we've had an amazing battle over my career.
"I feel sorry for him, but I want to keep my level tonight. I was playing superb tennis and I'm happy to be back."
Wawrinka will play Daniil Medvedev in the quarter-finals after the Russian world number five beat Germany's Dominik Koepfer.
It will be Wawrinka's second Grand Slam quarter-final of the year after being knocked out of the French Open by Federer at the same stage.
Wawrinka and Medvedev have played each other once, with the Russian claiming a 6-4 3-6 6-4 6-1 first-round win at Wimbledon in 2017.
"If you follow tennis, you've been watching him a lot - he's been playing final after final and won in Cincinnati," Wawrinka said.
"He's playing amazing tennis, he's a great athlete.
"It's going to be an interesting match. I'm happy to be in a quarter-final, happy to be against him and I'm looking forward to it."