A rash of injuries struck the U.S. Open men's draw on Monday, with Nicolas Kiefer succumbing to a wrist injury, Sargis Sargsian fighting through knee trouble and Andrei Pavel withdrawing with a back problem. All three finished the day out of the tournament -- Kiefer retiring against Tim Henman, Sargsian being picked off by Andre Agassi and Pavel exiting before his match with Roger Federer.

Agassi, the sixth seed, had little trouble with Sargsian, taking the match in a quick 6-3, 6-2, 6-2. The win sends Agassi to a quarterfinal matchup with No. 1 seed Federer, who got a free pass when No. 16 Pavel determined the pain from a disk in his back was too great.

"I never expect to win easily, and I think matches have the potential of looking that way more than feeling that way," Agassi said. "Sarge hasn't won four matches for no reason here. . . . He played some great matches. I just wanted to take care of business in tough conditions."

Sargsian was seen by the ATP doctor during the second set after his knee gave out on a serve. He was overloaded with tennis during the past two rounds, setting the record for longest consecutive matches, with a 5-hour 9-minute victory over Nicolas Massu followed by a 4:44 defeat of Paul-Henri Mathieu.

Agassi's win, in just 1:30, was primarily a result of Sargsian's 43 unforced errors; Agassi had 19.

After four-plus sets and 3:41, Kiefer retired from his match against Henman, giving the Briton a birthday gift -- his first trip to the quarterfinals of the U.S. Open.

The fifth-seeded Henman led Kiefer 6-7 (7-5), 6-3, 6-1, 6-7 (7-4), 3-0 when the German had to leave the match with an injury to his right wrist that left it swollen and powerless. An MRI exam showed a slight tendon tear. He'll be out three to six weeks.

Henman, who was celebrating his 30th birthday, failed to capitalize on many chances throughout the match by allowing Kiefer to save 17 of 25 break point opportunities.

Kiefer, the No. 19 seed, became frustrated midway through the fourth set, nearly three hours into the match. He smashed a ball into the stands, prompting a point penalty. The German continued to bark at the chair umpire, screaming about another questionable call that would have given him a set point a few games later.

"I came out very strong, then I let him play a little bit of his game," Kiefer said. "It was tough for me to focus today, I don't know why. I was struggling a bit with my serve. . . . The most important thing for me in this stage was that I kept fighting. Today, I stayed in by fighting and being positive, not by playing tennis."

No. 22 Dominik Hrbaty took out Olivier Rochus, sending the Belgian home after a Cinderella run to the fourth round. The 100th-ranked player went down in five sets, 2-6, 3-6, 6-3, 6-4, 6-0.