Players, fans and television announcers all continue to marvel at the same wonder at the U.S. Open. They watch Andre Agassi, the oldest player in the men's singles draw at 34, and see his feet dance, his groundstrokes sizzle.

They wonder about his legs, his shoulders and his flexibility. "Physically," former rival Jim Courier said, "you have to wonder how he can still do it at this age."

More intriguing, though, is why he still wants to.

Agassi advanced to the third round on Thursday, winning 7-5, 2-6, 6-2, 0-1 before his opponent, Florian Mayer, retired with a hamstring injury. On a day when the French Open men's and women's champions lost and blamed their defeats on fatigue, a bouncy, energetic Agassi advanced to the weekend for the 14th time in 19 U.S. Open appearances.

Meantime, two younger Americans, Taylor Dent and Mardy Fish, lost in the second round Thursday.

Agassi is considered a major threat to win because he has maintained his foot speed, his reaction time and his legendary ability to return serve. He has also maintained his desire, which impresses peers most.

"There are a lot of times when it sort of hits you, how long you've been out here," Agassi said. "But I'm not retiring at the end of this tournament. . . . I still love what I'm doing."

Whenever he does retire, he will take a long legend with him. He has won more than 60 titles, including eight majors. He helped reinvigorate the men's game with his dynamic rivalry with Pete Sampras, who is a year younger but has been retired for two years.

Agassi was one of the game's most recognized players as a long-haired, loud-mouthed 17-year-old and now he's still one of the game's most recognized players as a bald, mellow 34-year-old. His desire to win remains every bit as strong, he says.

"I love the challenge, and I want to win just as bad," Agassi said. "You've got a lot of guys out here with a lot of weapons that they bring to the table. I enjoy that. It really keeps me going."

Agassi's life is filled with signals to retire. He's married to former tennis star Steffi Graf, and the couple has two children. His main longtime rival, Sampras, is no longer playing. Already at this U.S. Open, Agassi has listened to two more younger players -- Wayne Ferreira and Todd Martin -- announce their retirements.

Yet Agassi needs tennis and tennis needs him. Agassi's the most popular player in the men's game, an aging yet still graceful ball of energy with the singular ability to turn spectators into fans. When he won a close first set Thursday, the Arthur Ashe Stadium crowd erupted.

Fans did the wave. They sang "Ole." They chanted Agassi's name until a befuddled chair umpire asked them -- no, begged them -- to quiet down. "To me," Mayer said, "they seemed very loud."

They'll only grow louder as this tournament progresses. Most players here see Agassi as one of four men capable of winning the tournament, along with Roger Federer, Andy Roddick and Lleyton Hewitt. If Agassi and Federer win two more matches, they'll meet in a highly-anticipated quarterfinal.

Agassi, though, may be the most feared player in the draw. He works harder to stay in shape now than he ever did before, and that's clear on the court. His foot speed hasn't lagged, and neither has his serve, which sometimes flies upward of 130 mph. "From his shots, age is no problem," Mayer said. "He has the best shots of all the players."

Notes: Gaston Gaudio and Anastasia Myskina, this year's French Open winners, became the highest-seeded players to exit. Myskina, the No. 4 seed, lost to Anna Chakvetadze, 7-6 (7-3), 6-3. Gaudio, the men's No. 9 seed, lost to Thomas Johansson, 6-3, 2-6, 6-4, 6-4. . . .

Top-seeded Justine Henin-Hardenne again barely survived her cold, and her opponent, in the second-round match, needing three sets to beat Tzipora Obziler, 6-2, 5-7, 6-2. "For sure, the last few days I haven't been feeling well," Henin-Hardenne said. "I couldn't practice as I wanted, I had to take antibiotic and everything, so it doesn't help to be at your best level." . . .

Tenth-seeded Nicolas Massu lost to Sargis Sargsian in a five-set match that lasted 5 hours 11 minutes, the second longest in U.S. Open history.