NEW YORK — Everyone's been curious about the condition of Rafael Nadal's knees, so it made sense that his first Grand Slam opponent in three months would wonder as well.

Which might explain why Richard Gasquet tried a drop shot deep in the third set of his U.S. Open match against Nadal yesterday. Nadal made the long run necessary to get to the ball, and flipped it back over the net, winning the point.

A moment later, as if conspiring with Nadal to show everyone how fit the six-time major champion truly is these days, Gasquet offered up another drop shot.

Nadal got to that one, too.

Starting a bid to win the only Grand Slam title missing from his resume, the third-seeded Nadal encountered no apparent trouble from his much-scrutinized legs in a 6-2, 6-2, 6-3 victory over Gasquet at Flushing Meadows.

Gasquet, for one, was impressed.

"He can win the tournament," said Gasquet, a 2007 Wimbledon semifinalist and former top-10 player. "Day after day, he will improve his level. For sure, he can win."

Nadal's matter-of-fact assessment: "I played well, no?"

Top-seeded Roger Federer's bid for a sixth consecutive U.S. Open championship — and third Grand Slam title in a row this year — progressed with a 6-3, 7-5, 7-5 victory over Simon Greul of Germany in front of a night-session record crowd of 24,206.

Next for Federer is a matchup against two-time major winner Lleyton Hewitt, who beat Juan Ignacio Chela, 6-3, 6-3, 6-4.

Defending women's champion Serena Williams was spectacularly good in eliminating 51st-ranked Melinda Czink of Hungary, 6-1, 6-1, in 53 minutes in last night's final match.

Sister Venus Williams, the 2000-01 champion in New York, easily dispatched Bethanie Mattek-Sands of the United States, 6-4, 6-2.

Kim Clijsters was away for two years, having ended her retirement in August, and she continues to play as if she never left.

Unseeded and unranked and playing at the U.S. Open for the first time since winning the 2005 title, the 26-year-old Belgian reached the third round by knocking off No. 14-seeded Marion Bartoli, 5-7, 6-1, 6-2.

Two fixtures on the men's tour said goodbye to Grand Slam tennis with first-round exits: Marat Safin of Russia and Fabrice Santoro of France, who are retiring at the end of the season.

The 29-year-old Safin, the 2000 U.S. Open champion, lost to Jurgen Melzer of Austria, 1-6, 6-4, 6-3, 6-4. The 36-year-old Santoro, appearing in his record 69th major tournament, was beaten by No. 24 Juan Carlos Ferrero of Spain, 6-4, 6-3, 6-3.