Defending champion Novak Djokovic is out of the US Open after quitting because of injury against Swiss 23rd seed Stan Wawrinka as defeat loomed in an electrifying fourth-round match.
Djokovic, 32, retired with a shoulder problem seconds after a double fault left him two sets and a break down.
Loud boos greeted the Serb’s decision, with more heard as he walked off court.
“I’m sorry for the crowd. They came to see a full match but it wasn’t to be,” said world number one Djokovic.
Three-time Grand Slam champion Wawrinka had dominated the last-16 contest in a boisterous atmosphere at Arthur Ashe Stadium, producing a powerful display reminiscent of his best to lead 6-4 7-5 2-0, when Djokovic decided he could not continue.
Wawrinka, 34, will play Russian fifth seed Daniil Medvedev in the quarter-finals.
Djokovic was the hot favourite to retain his title at Flushing Meadows and win a 17th Grand Slam, which would move him closer to Roger Federer (20) and Rafael Nadal (18) in the race to be deemed the greatest men’s player of all time.
But he had been hampered throughout the tournament with a left shoulder injury, which he says has left him in “constant pain for a few weeks”.