PARIS -- Venus Williams lost again in a Grand Slam tournament, only this time it wasn't against her sister.

The third-seeded Williams squandered an early lead and was beaten by 18-year-old Russian Vera Zvonareva 2-6, 6-2, 6-4 in the fourth round at the French Open.

	Venus Williams said that she either went for too little or not enough.

Williams had lost to sister Serena in the past four major events, including last year at Roland Garros.

Jennifer Capriati, the 2001 champion who was seeded seventh, also was upset by a Russian. Nadia Petrova, ranked 76th, won 6-3, 4-6, 6-3, then celebrated by punching the air and blowing a kiss to the crowd.

Zvonareva was not quite so expressive. When Williams yanked a backhand wide on match point, the Russian simply walked to the net, where she was greeted with a handshake and smile from her opponent.

"Maybe I'm just too tired to be excited,'' Zvonareva said. "You can win if you go to the court and believe it.''

She has climbed from 371st in the rankings at the beginning of last year to 21st entering the French Open.

"She did real well,'' Williams said. "She definitely stepped in there, and I had definitely a lot of opportunities. I felt like sometimes I went for too much or went for too little.''

Sister Serena emerged unscathed from a first-set scare and a nasty spill to beat Ai Sugiyama 7-5, 6-3. The match was much more arduous than Serena's 6-0, 6-0 victory over Barbara Schett in the previous round.

"I just wasn't hitting my shots the way I was the other day,'' the younger Williams said. "I was a little upset with myself. But it helps me -- it's nice to have a tougher match under your belt.''

Sixth-seeded Lindsay Davenport was forced to quit, aggravating a strained toe on her left foot that has bothered her for about a month. She was trailing No. 24 Conchita Martinez 6-4, 2-0.

Venus Williams entered the match well aware of Zvonareva, who pushed Serena Williams to three sets in the fourth round at Roland Garros last year.

The match was a backcourt slugfest. Zvonareva, seeded 22nd, went skidding into both corners retrieving shots to keep rallies going, often until her opponent made a mistake.

Williams committed 75 unforced errors and hit 12 double-faults to account for 87 of the 100 points Zvonareva won. Williams was broken six times.

Zvonareva held to reach 4-all in the final set, hit a forehand winner on the baseline to break for 5-4, then served out the match. Williams lost six of the last seven points and committed four errors in the final game.

"Each match is tough if it's a loss, especially if it's a Grand Slam,'' Williams said. "They're all really disappointing.''

The tournament was the first for Williams since an abdominal strain forced her to stop playing during the final May 4 in Poland.

"I don't think I had the kind of preparation I wanted,'' Williams said. "I just wasn't able to do all the things that I would normally like to do.''

Serena Williams was down a service break twice in the first set against Sugiyama but rallied from a 4-2 deficit. She escaped injury in the sixth game when she slipped on the clay chasing a shot and tumbled into the net, landing hard on her left side.

The victory was the 32nd in a row in Grand Slam events for Williams, who has beaten sister Venus in the past four major finals. Her opponent Tuesday will be France's Amelie Mauresmo, who upset Williams in the Rome semifinal May 17.

"She's definitely going to have the crowd on her side,'' Williams said. "I'm just going to go out there and do my best and really enjoy myself. I've played in the most hostile arenas possible, so it definitely won't bother me at all.''

Mauresmo, seeded fifth, advanced by beating Magui Serna 6-1, 6-2 but knows she'll have her hands full against Williams.

"Four Grand Slams in a row -- what can you say except total respect?'' Mauresmo said. "You've really got to try and get your head clear of all the media hype around the Williamses, and realize that these are not players from outer space.''

Martinez, at 31 the oldest player remaining in the women's draw, advanced against a hobbled Davenport, who said her toe began bothering her early in the match.

Martinez will next face No. 2 Kim Clijsters, who played 24 minutes before winning a game, then raced past No. 15 Magdalena Maleeva 0-6, 6-2, 6-1.

Chanda Rubin reached the quarterfinals at Roland Garros for the third time, beating Petra Mandula 4-6, 6-2, 7-5. The eighth-seeded American next plays No. 4 Justine Henin-Hardenne, who celebrated her 21st birthday by beating No. 19 Patty Schnyder 6-3, 2-6, 6-2.