PICS: Shoulder injury puts Djokovic out of US Open

Defending champion retires from fourth round match against Stan Wawrinka trailing 4-6, 5-7, 1-2.

Images from Day 7 at the US Open.

Novak Djokovic's US Open title defence came to a halt on Sunday after he retired from his fourth round match against Stan Wawrinka due to a shoulder injury.

Wawrinka was leading 6-4 7-5, 2-1 when world number one Serb, who won four of the last five Grand Slam titles, decided he could not continue and walked off the Arthur Ashe Stadium court to a chorus of boos.

After dropping the second set, Djokovic immediately called for medical attention and sat court side without his shirt on while the trainer massaged his shoulder.

He returned to the court but was still clearly hampered by the issue before calling it a day.

"It's never the way you want to finish a match," said Wawrinka. "I am really sorry for Novak, he's an amazing friend."

The shoulder issue flared up earlier this week and nearly saw Djokovic knocked out in the second round on Wednesday but the 32-year-old seemed to have recovered by Friday when he won in straight sets to reach the last 16.

"I don't want to talk about my injuries," Djokovic told reporters. "I've said that in the past. I am sticking to that."

Up next for Wawrinka is Russian fifth seed Daniil Medvedev, who beat German qualifier Dominik Koepfer 3-6, 6-3, 6-2, 7-6(7-2) earlier on Sunday to reach his first Grand Slam quarter-final.

Federer too good for Goffin

Roger Federer destroyed David Goffin 6-2, 6-2, 6-0 on Sunday to reach the US Open quarter-finals and keep his bid for a record-extending 21st Grand Slam title alive.

The Swiss third seed fired 35 winners and 10 aces to see off the outclassed Belgian in a speedy 80 minutes on a sunny day at Arthur Ashe Stadium.

The 38-year-old Federer was at his best when it mattered most, converting nine of his 10 break point opportunities to set up a meeting with Grigor Dimitrov or Alex de Minaur, who were playing their round of 16 match on the Grandstand court.

The only drama came early when Goffin, seeded 15th, broke Federer to take a 2-1 lead in the first set but the Swiss broke back in the next game and cruised to the finish line.

"I'm very happy with the level of play and the atmosphere," Federer said in an on-court interview.

Svitolina serves her way past Keys

Ukrainian fifth seed Elina Svitolina delivered a solid serving performance to beat American Madison Keys 7-5, 6-4 on Sunday and secure a spot in the quarter-finals.

With Keys, who finished runner-up in 2017, struggling with her backhand, Svitolina won 92 percent of her first serve points and did not face a single break point during the 75-minute clash under the Arthur Ashe Stadium lights. 

“Very pleased that I could play very consistent tonight and in such a great atmosphere is very special,” said Svitolina, who capped the match in style when she served out to love.

With the win, Svitolina is the first Ukrainian woman to reach the US Open quarter-finals since Kateryna Bondarenko in 2009.

Up next for Svitolina will be Briton Johanna Konta, who upset Czech third seed Karolina Pliskova earlier on Sunday.

British No.1 Konta dropped the first set on a tie-break but battled back to win 6-7(1-7), 6-3, 7-5.

Serena advances despite ankle injury

Serena Williams needed a medical time out in the second set of her 6-3, 6-4 win over Petra Martic on Sunday to get treatment on her right ankle but recovered to advance to the quarter-finals.

Williams fell to the court at 2-2 in the second set after charging to the net to hit a volley that sailed long.

The 37-year-old American eighth seed got treatment on her ankle during the changeover and appeared to be fine, smacking 38 winners on a sunny day at Arthur Ashe Stadium court.

Williams blasted her fourth ace on match point to see off 28-year-old Croatian Martic and reach the last eight, where she will face Wang Qiang of China for the first time.

Barty thrashed by Wang

Second seed Ashleigh Barty’s US Open bid came crashing down when she lost 6-2, 6-4 to China’s Wang Qiang in the fourth round.

Wang had never taken a set off the former world number one in two previous matches and looked to be in trouble after Australian Barty started with a dominant performance on serve.

But 18th seed Wang kept her composure and took advantage of 25 more unforced errors by Barty to reach the quarter-finals of a Grand Slam tournament for the first time.