Defending US Open champion Novak Djokovic retired three games into the third set after dropping the first two to Stanislas Wawrinka in the fourth round on Sunday night.
Djokovic has been bothered by a shoulder injury throughout the tournament.
Wawrinka won the first two sets 6-4, 7-5 to take a large lead against Djokovic as he sought to beat him in their first meeting since the 2016 US Open final.
Wawrinka had just broken Djokovic’s serve — winning four straight points — to go up 2-1 in the third set when Djokovic decided not to continue, much to the displeasure of the crowd at Arthur Ashe Stadium.
“Never the way you want to finish a match. I’m really sorry for Djokovic — he’s a good friend, he’s an amazing champion,” Wawrinka said after the match.
Following a final double-fault, the top-seeded Djokovic walked toward the chair umpire, nodded that he was done, and embraced Wawrinka, who advances to face No. 5-seed Daniil Medvedev in the quarterfinals.
Earlier, Djokovic blew a 4-1 advantage in the second set.