The Associated Press

NEW YORK - So now Roger Federer knows what it feels like to take to the court as a Grand Slam champion.

Kim Clijsters, still getting used to seeing "No. 1" next to her name, would love to be the proud owner of a major title, too.

Accustomed to shaky starts at Slams, Federer lost his first set Wednesday at the U.S. Open, then took control against Jose Acasuso and eventually advanced to the second round when the Argentine quit because of pain in his groin and back. The official score was 5-7, 6-3, 6-3, 2-0, ret.

Clijsters followed in Arthur Ashe Stadium and had a much easier time, overpowering Laura Granville of Chicago 6-1, 6-1 to reach the women's third round, where she was joined by 1998 Open champion Lindsay Davenport.

"If it's in their head they're playing the No. 1, maybe that's a little bit intimidating," Clijsters said. "On the other hand, that could even be also more motivating as well. I think it depends on the character of your opponent."

The man Federer beat in the Wimbledon final, No. 20-seeded Mark Philippoussis, won his first-round match Wednesday, as did 2002 Wimbledon runner-up David Nalbandian, No. 7 Carlos Moya and No. 10 Jiri Novak. Philippoussis, also a finalist at the 1998 U.S. Open, pounded 20 aces to beat Janko Tipsarevic 6-2, 7-6 (4), 6-4.

Davenport, the only past champion in the women's field, won in straight sets again despite a left foot injury for which she'll have surgery after the tournament. She beat Maria Elena Camerin, an Italian ranked 92nd in the world, 6-2, 6-4. It wasn't a perfect outing, but Davenport will take it. She put in just 46 percent of her first serves, and her unforced errors outnumbered winners 23-22.

"The main thing is, my foot didn't hurt, and I'm on to the third round," Davenport said.

The No. 2-seeded Federer snapped a run of three first-round losses in five majors when he won Wimbledon last month with a brand of all-court play that earned him comparisons to Pete Sampras.

The victory at the All England Club also lifted the burden of expectations that Federer acknowledged weighed on him since upsetting Sampras at Wimbledon in 2001. Sampras, of course, formally retired this week.

"These are big names retiring right now. It's been taking a long time now, the changing of the guard," Federer said. "I always thought we were a good group of guys, the youngsters. We've proved it now. We've won Grand Slams."

Clijsters seems to be on the verge of being able to make the same claim.

But when the Belgian replaced Serena Williams atop the WTA Tour computer rankings Aug. 11, she was the first woman to get to No. 1 without winning a Slam title.

That's not to say Clijsters hasn't played superbly, reaching the semifinals at 14 of her 15 tournaments in 2003 and tying for the tour lead with six titles. She lost to Williams in the Australian Open semifinals, to Justine Henin-Hardenne in the French Open final and to Venus Williams in the Wimbledon semifinals.

Serena Williams doesn't begrudge Clijsters the top ranking. Williams, unable to defend her U.S. Open title because of left knee surgery, has entered only seven events this season.

Clijsters, Williams said Wednesday, is "playing every week. It's hard not to be No. 1. She's winning almost every week that she plays."

Williams did suggest that the tour count 12 instead of 17 tournaments for a player over a 52-week period. Playing too often, she said, "it's hard to stay injury-free."