PARIS — With twilight descending, Venus Williams watched one final shot land out of reach, ending a bad day for her family — and for U.S. tennis.

Williams and her sister Serena were eliminated in third-round matches today at the French Open. Serena lost to Katarina Srebotnik 6-4, 6-4, and more than eight hours later Venus was beaten by Flavia Pennetta 7-5, 6-3.

The double defeats meant that for the first time in the Open era, there will be no American woman in the fourth round at Roland Garros. The only U.S. player left is Robby Ginepri on the men's side.

Winners of 14 Grand Slam titles, the Williams sisters lost to two tour veterans who have never reached a major quarterfinal.

For Serena, missed opportunities came in a flurry. She shanked overheads, hit wild volleys and squandered six break points.

But Venus never really gave herself a chance, losing serve six times and committing 29 unforced errors as Pennetta repeatedly bested her in long rallies.

To beat the older Williams, Pennetta had to beat darkness, and she closed out the victory with a forehand winner at 9:47 p.m. Seeded 26th, Pennetta advanced to the fourth round at Roland Garros for the first time.

Serena's hasty exit matched her earliest in nine visits to Roland Garros and guarantees a first-time women's champion. Williams, who won the French Open in 2002, was the lone former champion to enter the draw.

"I missed a lot of easy shots and a lot of key points that I felt like could have turned the match around," a subdued Serena said. "I wasn't able to capitalize."

Three-time defending champion Rafael Nadal played for the fourth consecutive day in the rain-interrupted tournament and defeated Jarkko Nieminen 6-1, 6-3, 6-1 to reach the fourth round. No. 3-seeded Novak Djokovic beat Wayne Odesnik 7-5, 6-4, 6-2.

Top-seeded Maria Sharapova and No. 2 Ana Ivanovic advanced. In the completion of a second-round match halted in the second set Thursday because of darkness, Sharapova beat American Bethanie Mattek 6-2, 3-6, 6-2. Ivanovic reached the fourth round by beating 17-year-old Caroline Wozniacki 6-4, 6-1.

Serena Williams, who played the day's first match on Court Suzanne Lenglen, converted only one of seven break-point chances and was 0-for-5 in the second set. She repeatedly set up points but failed to finish them, losing 14 of 21 at the net.

"There are a lot of things I would try to do different, but you can't rewind time," said Williams, who also lost in the third round at Roland Garros in 1999.

Her mother and coach, Oracene Price, said Williams has "been in a funk. It's not like her. She wasn't herself."

Srebotnik, seeded No. 27, earned the biggest victory of her career. She has only one win over a player ranked higher than the No. 5-ranked Williams, beating No. 4 Amelie Mauresmo at Zurich in 2005.

Williams didn't play like a top player. In the final game of the first set, she dumped an easy overhead into the net. Four points later, she worked her way forward but blew a volley, then bent over in dismay and pressed her forehead against the tip of her racket handle.

Another botched overhead cost her in the sixth game of the second set, helping Srebotnik to reach 3-3.

"I wasn't nervous," Williams said. "She was getting a lot of balls back, and I might have let that get into my head. She was just making some shots I don't think she's ever made before, or she probably would be in the top two."

When Williams fell behind she turned up the volume, grunting with almost every shot and screaming in celebration when she hit a winner. But she was unable to rally, and her 27-year-old opponent kept her cool down the stretch.

"Today I woke up and it was just another opportunity," Srebotnik said. "This is what you work so hard for — to be in third round where you play Serena or someone like that and you have really nothing to lose."

Srebotnik credited her tactics for the upset, mixing the pace of her ground strokes to keep Williams off balance.

"That was the rhythm that I was trying ... to get her on a wrong foot and stuff like that," Srebotnik said. "When she's serving well, she's very tough, but once I got in the rally I had no problem playing her."

In the second set, Williams hit an ill-advised drop shot into the net to lose serve and fall behind 5-4. She saved two match points in the next game, but on the third yanked a forehand wide for her 25th unforced error, then met Srebotnik at the net with a grin and handshake.

Williams sat dejected at her postmatch news conference, explaining her demeanor by saying, "I just don't want to be here."

Among those staying for the fourth round was No. 10 Patty Schnyder, who defeated Emilie Loit 7-6 (4), 5-7, 6-2. No. 11 Vera Zvonareva and No. 25 Nadia Petrova completed rain-interrupted, second-round wins.

On the men's side, No. 10 Andy Murray was eliminated by No. 19 Nicolas Almagro 6-3, 6-7 (3), 6-3, 7-5, and No. 15 Mikhail Youzhny lost to No. 22 Fernando Verdasco 7-6 (5), 5-7, 7-5, 6-1.

Sharapova won despite 10 double-faults, giving her 27 in two matches. She finished with 51 unforced errors as she struggled to find a comfort level on clay, her least-favorite surface.

The French Open is the only Grand Slam she has yet to win.

"You're going to have to hit more balls, and you're going to have to move a few extra steps to the ball," Sharapova said. "You have to be more patient. I'm definitely getting better at that, and I'm getting smarter out there."

Nadal, who has been bothered this spring by a blister on his right foot, requested treatment by a trainer after the second set. He said he wanted to keep the ailment from becoming serious, and it didn't prevent him from winning in straight sets for the third time this week.

"I controlled the match from A to Z," he said. "I didn't struggle at all, which is a good sign."