(Reuters) - Novak Djokovic's U.S. Open title defence ended in agony on Sunday when the Serb retired from his fourth round match against Swiss Stan Wawrinka because of a shoulder injury.
Wawrinka converted his fourth break point to lead 6-4 7-5 2-1 when world number one Djokovic, who received treatment on his left shoulder after the second set, decided he could not continue.
"It's never the way you want to finish a match. I'm really sorry for Novak," said Wawrinka, who defeated the Serb in the 2016 final to lift the title.
"We've played amazing battles all of my career. I want to keep my level (from) tonight. I was playing super good tennis. I'm happy to be back."
Wawrinka has reached the quarter-finals at Flushing Meadows for the fifth time in his last six appearances, and will next face Russian Daniil Medvedev.
Third seed Roger Federer produced a clinical display to beat Belgium's David Goffin 6-2 6-2 6-0 in 79 minutes.
Federer has steadily improved his level in the tournament as he continues chasing a 21st Grand Slam trophy. Against Goffin, the 38-year-old struck 35 winners and made only 17 unforced errors.
In the women's draw, Serena Williams remained on track for a record-equalling 24th Grand Slam title despite needing treatment on her right ankle in a 6-3 6-4 win over Croatian Petra Martic.
American Williams rolled her ankle in the fifth game of the second set but recovered to set up a quarter-final clash against Wang Qiang of China.
Britain's Johanna Konta came back from a set and 3-1 down to beat Czech third seed Karolina Pliskova 6-7(1) 6-3 7-5.
In her first U.S. Open last-eight appearance, Konta will take on Elina Svitolina after the Ukrainian beat home favourite Madison Keys 7-5 6-4.
0240 DJOKOVIC RETIRES INJURED IN THIRD SET, WAWRINKA THROUGH
Swiss Stan Wawrinka booked a spot in the quarter-finals after defending champion Novak Djokovic retired with a shoulder injury, trailing 6-4 7-5 2-1.
Wawrinka, the 2016 champion, will next face Russian Daniil Medvedev.
0035 SVITOLINA UNLOCKS KEYS TO ADVANCE
Fifth seed Elina Svitolina beat American Madison Keys 7-5 6-4 to reach the U.S. Open quarter-finals for the first time.
Keys hit seven aces, but made three times as many unforced errors as the Ukrainian, who will play Johanna Konta next.
0015 MEDVEDEV BEATS KOEPFER IN FOUR SETS
Fifth seed Daniil Medvedev bounced back after losing the first set to beat Germany's Dominik Koepfer 3-6 6-3 6-2 7-6(2).
Both players made a high number of unforced errors, with Medvedev (45) slightly better than Koepfer (51) on that count, but the Russian served 15 aces to his opponent's two and will face Novak Djokovic or Stan Wawrinka in the quarter-finals.
2115 BRYAN FINED FOR MAKING SHOOTING GESTURE WITH RACKET
Mike Bryan has been fined $10,000 for making a shooting gesture with his racket aimed at a line judge during a second- round doubles match on Saturday.
The 41-year-old American turned his racket upside down and pointed it at the judge after the official made a wrong call in the second set of his match against Roberto Carballes Baena and Federico Delbonis.
2000 SERENA TOO STRONG FOR MARTIC
Eighth seed Serena Williams fought through the pain of a twisted ankle which needed lengthy treatment to beat Petra Martic of Croatia 6-3 6-4 in the last 16.
The American former world number one scorched the court with 37 winners and will face China's 18th seed Wang Qiang in the quarter-finals.
1940 DIMITROV BEATS DE MINAUR
Bulgaria's Grigor Dimitrov beat Australia's Alex de Minaur 7-5 6-3 6-4 to set up a quarter-final clash with Roger Federer.
Dimitrov won 79% of his first-serve points and hit 31 winners to reach the U.S. Open last eight for the first time.
1915 KONTA INTO QUARTERS AFER BEATING PLISKOVA
Britain's Johanna Konta reached her third consecutive Grand Slam quarter-final after beating third seed Karolina Pliskova 6-7(1) 6-3 7-5.
The 16th seed hit 45 winners, nine more than Pliskova, and won nine points at the net. She will face either Elina Svitolina or Madison Keys in the last eight.
1736 FEDERER CRUISES PAST GOFFIN
Third seed Roger Federer was barely tested in his fourth- round match against David Goffin, beating the Belgian 6-2 6-2 6-0 at Arthur Ashe Stadium to advance in 79 minutes.
Federer converted nine of 10 break points, won 19 net points and hit 35 winners (27 more than Goffin) to move into his 56th Grand Slam quarter-final.
1632 BARTY UPSET BY WANG IN STRAIGHT SETS
Second seed Ash Barty lost 6-2 6-4 to China's 18th seed Wang Qiang, who advanced to her first Grand Slam quarter-final by dispatching the French Open champion in 82 minutes.
Wang claimed victory on her third match point after Barty had saved two on her own serve, but 39 unforced errors by the Australian, who did not convert a single break point, saw her make an earlier than expected exit in New York.
1510 PLAY UNDERWAY IN NEW YORK
Play began on Sunday in cloudy conditions with the temperature hovering around 22 degrees Celsius (71.6°F) and a forecast high of 25C, with rain expected later in the day.
(Reporting by Rohith Nair, Simon Jennings and Hardik Vyas in Bengaluru, editing by Ed Osmond/Amlan Chakraborty)