NEW YORK -- Another injury struck the U.S. Open on Tuesday, and this one left unseeded Magnus Norman with an aching back and Gustavo Kuerten in the quarterfinals for the first time.

	USTA trainer Adam Tyson, left, helps Magnus Norman to his feet after Norman injured his back during his match.

Kuerten didn't seem as concerned with how he advanced -- he was just happy he had.

"Very lucky," said Kuerten, who was down a break in the opening set when Norman started to suffer the effects of the injury. "I think he was playing a little bit better than me. I was very, very lucky."

Norman is the seventh player in the men's draw to retire during a match. That group includes two-time defending champion and fourth seed Patrick Rafter and eighth seed Carlos Moya.

Todd Martin of the United States, did everything but give up during his match. Martin, the seventh seed, used a fifth-set outburst to roar past No. 9 Greg Rusedski of Britain, 5-7, 0-6, 7-6 (7-3), 6-4, 6-4.

Martin looked awful in dropping the first two sets but staged a comeback to notch his sixth win in seven all-time meetings with Rusedski, the 1997 runner-up here who remains without a title this season.

Rusedski won four of the first five games of the fifth set and appeared on his way to victory when Martin rallied. He won 18 straight points before double-faulting at 30-love in the 10th game. He recovered nicely with a pair of aces to close out the set.

Martin has reached at least the quarterfinals in 10 of 12 tournaments this season. He lost in the quarterfinals at both the Australian Open and Wimbledon.

Earlier this year, Martin beat Rusedski in straight sets of a first-round tie against Britain in the Davis Cup.

Norman was up a break and ready to serve for the opening set when he became the latest victim of injury. Kuerten came back to capture the first set by winning 7-4 in a tiebreaker and was leading in the first game of the second set when Norman decided to call it quits.

Kuerten's next opponent will be 1993 U.S. Open finalist Cedric Pioline of France, who Tuesday upset 14th seed Tommy Haas of Germany, 6-4, 7-5, 6-3.

Norman suffered the injury at 5-5 in the opening set. He chased down Kuerten's drop shot at break point, flicked a winner into the open court and pumped his first to celebrate the first break of serve in the match. But as he rose from his chair during the ensuing changeover, he reached for his back and called for a trainer.

"It was not that last point when I broke him. It was the point before," Norman explained. "I heard a click in the back when I was going to return the serve at 30-40. I felt an unbelievable amount of pain. I broke for 6-5, but when I came to the chair, I said, 'This is not right.' I had never felt that way before."

After receiving on-court treatment, Norman attempted to serve for the set, but was broken at love. Kuerten then raced to a 5-1 lead in the tiebreak. Norman received treatment again after losing the tiebreak and served to open the second set. He gave up after hitting a forehand into the net on the third point of the first game.

"I spoke to the doctor and he said it was bad luck. There's not much I could do," Norman said. "It's a shame. I have been playing the best tennis of my life and thought I had an opportunity today."

Norman was one of the more active players during the summer hardcourt season. He played in five tournaments in the six weeks preceding the Open and had won 21 of his last 23 matches, including tournament titles at Stuttgart, Umag and Long Island.

"There are a lot of tournaments before the Open," said Kuerten, attempting to explain the rash of injuries. "Some guys play a lot before coming here. Then we have to go out and play three-of-five sets, spend three or four hours on the court."

Pioline took advantage of a weakened Haas, who has battled a hip flexor injury since his first-round match. The Frenchman was down a break in both the first and second sets, but rallied back each time.

"If you're up a break, you got to try and hold it," Haas said. "I started off the first and second set with a break. If I can't finish off those sets in the round of 16 in a match in a Grand Slam, that's tough."

Pioline played solid tennis throughout while Haas struggled in the windy conditions. Pioline won a whopping 88 percent of points played on his first serve, dominated at the net and hit 35 winners, two more than his unforced errors. Meanwhile, Haas committed 45 unforced errors, the last on Pioline's second match point.

"It was difficult to play out there because of the wind," said Pioline. "I think I'm much better with the wind because I try to mix up my game a little bit."

"I don't know if he was difficult today. I think it was more the tough conditions, the wind," Haas said. "I had a tough time getting a little bit used to that."

In another men's match today, Slava Dosedel defeated fellow unseeded countryman Jiri Novak, 6-4, 7-5, 5-7, 7-5 to become the first Czech to advance to the U.S. Open quarterfinals since Petr Korda in 1997. The Czech Republic has had a player in the U.S. Open quarterfinals four of the past six years.

Dosedel will play Martin.