Novak Djokovic’s US Open title defence is over and the tennis world appalled at the clueless display by spectators at Arthur Ashe Stadium who booed the world No.1 as he left the court.

Succumbing to a shoulder injury in his round of 16 clash with Stan Wawrinka, Djokovic seemed to take the catcalls in his stride, giving the crowd a thumbs-up.

John McEnroe, calling the game on ESPN, condemned the crowd for the boos, with social media lighting up in support of Djokovic, who has often failed to attract the same level of support as much-loved contemporaries Roger Federer and Rafael Nadal

The incident came only days after Daniil Medvedev trolled a booing crowd after his victory over Spaniard Feliciano Lopez saying he won the match “because of you”.

Medvedev had earlier angered the crowd with a petulant display, but there seemed no good reason boo a player of Djokovic’s standing, particularly given he was clearly struggling with injury.

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With the Swiss leading 6-4 7-5 2-1, Djokovic decided he could not continue after dropping his serve for the fourth time in the match.

The top-seeded Serb has been troubled by a painful left shoulder during the past week at Flushing Meadows and appeared uneasy during the one-hour-and-46-minute match.

“It is never the way you want to finish a match. He is an amazing champion and we had amazing battles in the past,” Wawrinka said in his on-court interview.

“It has really been tough since my surgery. It feels amazing to be back at this level.”

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It is Djokovic’s earliest exit at the New York grand slam since a third-round loss in 2006 to Australia’s Lleyton Hewitt.

Wawrinka, who beat Djokovic in the 2016 US Open final, advanced to a quarter-final clash with in-form Medvedev.

The fifth-seeded Russian came from a set down to knock off German qualifier Dominik Koepfer 3-6 6-3 6-2 7-6 (7-2) and reach his maiden grand slam quarter-final.

The New York crowd, angered by what tournament organisers called Medvedev’s ‘visible obscenity’ two nights earlier, were firmly behind Koepfer when he went a set and a break up.

But Medvedev kept his cool and eventually prevailed.

Earlier on Sunday, Roger Federer proved he has his groove back by destroying David Goffin to advance to his 13th US Open quarter-final.

After surprisingly dropping the opening set in his first two rounds, the Swiss cruised through his second easy straight-sets victory by belting David Goffin 6-2 6-2 6-0 in less than 80 minutes.

Roger Federer in action against David Goffin. Photo: Getty

“Sometimes these scores just happen,” Federer told reporters.

“You catch a good day, the opponent doesn’t, then things happen very quickly.

“I found my groove after a while and was able to roll really. Never looked back.”

Federer fired 35 winners and 10 aces to see off the outclassed Belgian.

The 38-year-old third seed was at his best when it mattered most, converting nine of his 10 break point opportunities to set up a meeting on Tuesday with Grigor Dimitrov, who outclassed Australian Alex de Minaur.

The Bulgarian was ruthless in his 7-5 6-3 6-4 win over 20-year-old De Minaur.

“There’s not much to say other than that I’m pleased to be back on a court, pain-free and feeling really good,” Dimitrov said in his on-court interview.

Although Federer holds a 7-0 head-to-head record over Dimitrov, the former world No.3 has taken sets off the Swiss on hard courts.

-with AAP