Top seed Roger Federer remains on course to win his third Grand Slam of the year after advancing to the quarter-finals at Flushing Meadows thanks to a walkover.
The 23-year-old took his place in the last eight following the withdrawal of fourth-round opponent Andrei Pavel through injury.
Pavel was forced out with a herniated disk in his lower back, which he sustained in the fifth set of a third-round victory over Hyung-Taik Lee of Korea.
“The disc is a bit damaged,” said Pavel, who learned of the severity of the injury when he got the result of an MRI this morning.
“It was a very big risk that if I played tonight it could be much, much worse and danger my career. So I don’t want to do that.”
The US Open was the only Grand Slam in which Federer had not reached the quarter-finals.
Federer will now await the winner of the match between 34-year-old Andre Agassi and the American’s close friend Sargis Sargsian of Armenia, an occasional practice partner.
Agassi has dropped only one set while Sargsian has survived five-set marathons totalling more than 10 hours over his last two matches.
The winner of the Lindsay Davenport versus Venus Williams match will face Shinobu Asagoe of Japan.
Asagoe advanced to her first Grand Slam quarter-final by outlasting number 29 seed Eleni Daniilidou of Greece 7-6 (7-4) 4-6 6-3.
Top seed and defending champion Justine Henin-Hardenne of Belgium is also in action as she tries to improve to 6-0 against number 14 Nadia Petrova of Russia in a night match at Ashe Stadium.
The 27th seed Mary Pierce of France, who enters fresh off a victory over Wimbledon champion Maria Sharapova, meets ninth-seeded Russian Svetlana Kuznetsova in another fourth-round encounter.
In another men’s match, number 22 seed Dominik Hrbaty of Slovakia plays Olivier Rochus of Belgium.