World number one Roger Federer made the US Open quarter-finals without hitting a ball after his opponent Mardy Fish withdrew for health-related reasons.
Five-time champion Federer will face Czech sixth seed Tomas Berdych for a place in the semi-finals in New York.
Berdych beat Spaniard Nicolas Almagro 7-6 (7-4) 6-4 6-1 in round four.
Twelfth seed seed Marin Cilic beat Slovakian Martin Klizan 7-5 6-4 6-0 to set up a quarter-final against Britain's Andy Murray.
Third seed Murray beat Canadian Milos Raonic 6-4 6-4 6-2 in their fourth-round match.
Fish was out for about two months earlier this season because of an accelerated heartbeat, and he had a medical procedure in May.
The 30-year-old American's third-round match against Gilles Simon went five sets, lasting more than three hours and finishing after 1am local time on Sunday.
Fish's agent, John Tobias, said: "We are not 100% sure what the issue is and if it is related to his previous issues."
"I was reluctant to [withdraw] but am following medical [advice]," said Fish in a statement.
"I had a good summer and look forward to resuming my tournament schedule in the fall."
"I am really sorry for Mardy," said Federer, who has now reached 38 Grand Slam tournament quarter-finals, three shy of the record 41 achieved by Jimmy Connors. "I just want to wish him a speedy recovery. We all want to see him back on tour soon.
"It will be a tough match against Tomas. We have played many times in the past and he has always been a tough opponent. I will have to continue to serve well and dictate the points."