Defending champion Novak Djokovic reached the US Open quarter-finals when Stanislas Wawrinka retired from their fourth-round match.
Djokovic was 6-4, 6-1, 3-1 ahead when the Swiss 18th seed called it quits, although the reason was not immediately apparent.
The Serb has now reached the quarter-finals for the sixth straight year and his 13th successive last-eight at a major.
The pair had begun their fourth-round clash on Tuesday night before rain brought a premature end to play and they were on and off the court again before the match finally resumed just after 1pm on Wednesday.
The last time the Swiss beat Djokovic was six years ago and when Wawrinka failed to hold serve straight after breaking things swiftly went downhill in the for the 18th seed.
After saving a break point in the opening game of the second set, Djokovic reeled off four games in a row, and Wawrinka responded by smashing his racquet on the court.
It did not help, though, and he was quickly a break down in the third set. Wawrinka talked to the trainer after the change of ends and, following the fourth game, he called Djokovic to the net and shook hands.
The World number two has dropped just 20 games in four rounds.
"I'm happy with my performances," said Djokovic, who played his match in front of just a few hundred fans.
"I played well against a quality opponent and I wish him a quick recovery."
He will next face either 2009 champion Juan Martin Del Potro, the Argentine seventh seed, or 2003 winner Andy Roddick for a place in the semi-finals.