WIMBLEDON, England - Walking away from Centre Court, Oracene Price - mother and sometimes-coach to Serena and Venus Williams - shook her head after watching one daughter lose at Wimbledon, then the other.

Undeniably great as she is, even defending champion Serena found it too tough to make a deep run at her first Grand Slam tournament in a year after a series of health scares. And as successful as Venus has been at the All England Club, even she couldn't muster her best after missing nearly five months with a hip injury.

"I don't think their layoffs helped their rhythm," Price said. "They both seemed to be making the same kinds of mistakes. They were hit-and-miss, here and there."

They're both headed home after straight-set exits in the fourth round against far-less-accomplished opponents Monday. First, 13-time major champion Serena lost 6-3, 7-6 (6) to ninth-seeded Marion Bartoli on Court 1. Then, less than two hours later and before a Centre Court crowd that included Prince William and his new bride, Kate, five-time Wimbledon champion Venus was beaten 6-2, 6-3 by 32nd-seeded Tsvetana Pironkova.

Adding to the chaotic nature of the afternoon, top-seeded Caroline Wozniacki lost, too, although she's still searching for her first Grand Slam singles trophy, whereas the Williams sisters own a total of 20.

"Definitely not our best day," Venus said. "I think we both envisioned seeing this day going a little bit different."

And why shouldn't they have? After all, Venus and her younger sister combined to win nine of the past 11 Wimbledon titles, including Serena's victories in 2009 and 2010. They even played each other in four of the finals in that span.

"Well, I never came here thinking I would lose," said Serena, a former No. 1 whose ranking now will plummet to about 175th. "That's my attitude."

It's the first time since 2006 that neither Williams is in the Wimbledon quarterfinals; Venus lost in the third round that year, while Serena skipped that tournament because of a left knee injury. Of the 12 years that both entered the field at the All England Club, this is the first neither one made it past the fourth round.

"Obviously, it's not something planned," Venus said. "We rarely lose on the same day."

That's true: They last lost on the same day at a Grand Slam tournament on May 30, 2008, in the French Open's third round.

All in all, it was a topsy-turvy day at the All England Club. Set aside, for a moment, what went on with the Williams sisters, and digest Monday's various other happenings:

• Wozniacki still has yet to make it past the fourth round at Wimbledon after a 1-6, 7-6 (5), 7-5 defeat against No. 24 Dominika Cibulkova;

• defending champion and top-seeded Rafael Nadal initially thought he broke his left foot and might have to quit late in the first set, then lost the second set, but eventually beat 2009 U.S. Open champion Juan Martin del Potro 7-6 (6), 3-6, 7-6 (4), 6-4;

• six-time Wimbledon champion Roger Federer dropped his first set of the fortnight - against a man he was 10-0 against, no less - before righting himself to reach a 29th consecutive Grand Slam quarterfinal;

• 18-year-old Bernard Tomic of Australia became the youngest man in the Wimbledon quarterfinals since 1986, when Boris Becker went on to win his second title in a row;

• 2010 runner-up Tomas Berdych went out in straight sets against 10th-seeded Mardy Fish, who never before reached the quarterfinals at the All England Club but now is the last American, man or woman, left in the tournament.

"Last. ... Not what you set out to do," said Fish, who is 0-5 against Nadal heading into their quarterfinal. "It was, I guess, bad luck for the Williams sisters to lose. Unfortunate, I guess. They'll be back, I'm sure."

They won't be around for the women's quarterfinals today, which are: Cibulkova of Slovakia vs. No. 5 Maria Sharapova of Russia; Bartoli of France vs. wild-card entry Sabine Lisicki of Germany; No. 8 Petra Kvitova of the Czech Republic vs. Pironkova of Bulgaria; and No. 4 Victoria Azarenka of Belarus vs. Tamira Paszek of Austria. It's the first time since 1913 that the last eight women at Wimbledon are from Europe - and, as it happens, eight countries are represented.

After a day off, the men play their quarterfinals Wednesday. In addition to Nadal vs. Fish - assuming Nadal decides to play after getting an MRI exam on his foot - the matchups are No. 2 Novak Djokovic vs. Tomic; No. 3 Federer vs. No. 12 Jo-Wilfried Tsonga; and No. 4 Murray vs. unseeded Feliciano Lopez.

"I'm worried, for sure," Nadal said.

Neither of the women who beat the Williams sisters Monday has won a Grand Slam title, although Bartoli did reach the Wimbledon final in 2007 - before losing to Venus. Pironkova, meanwhile, produced her best Grand Slam showing at the All England Club a year ago, when she made it to the semifinals by beating Venus - coincidentally, also by the score of 6-2, 6-3.

Pironkova also beat Venus at the 2006 Australian Open, yet somehow she clearly didn't make much of an impression on Mom.

"I don't even remember her playing her before. They said she lost to her here a year ago," Price said. "I didn't remember the girl. I'll remember her this time."

As well she should, because Pironkova befuddles the older Williams sister. On Monday, Pironkova played steadily, making only 10 unforced errors, half as many as Venus.

"Today's match probably looked easier on the outside, but it took me enormous amount of power to beat her," Pironkova said. "I kept pushing her. As I said, I played well. So she probably got a little shaky, and I took over."

Pironkova was 4-14 at tour-level events before her 4-0 run so far at Wimbledon.

Apparently, her game takes on a whole new depth on grass courts - and against Venus.

"It's kind of inexplicable why I manage to play some of my worst tennis against her," Venus said. "It's not like I'm intimidated at all by anybody on tour."

Perhaps, though, players are not as intimidated as they once were when facing a Williams.

Against Serena, Bartoli never backed down. Indeed, she took a page directly out of the sisters' playbook, moving a few feet inside the baseline to receive serves.

Serena insisted afterward she never noticed that, nor was she bothered by any of Bartoli's many eccentricities: gripping her racket with two hands for forehands and backhands; hopping on the balls of her feet between points; taking full-cut swings between points; swaying left and right before getting ready to return serves.

"It's a bit 'special,'" Bartoli said, making air quotes with her fingers. "But it's the way ... I'm feeling comfortable."

Over and over Monday, she'd whip deep groundstrokes to a corner, putting Serena on the defensive. Bartoli also served quite well, finishing with 10 aces and ending the match with a 103 mph service winner.

She's on a superb run right now.

In her three tournaments prior to Wimbledon, she reached the final at Strasbourg and the semifinals at the French Open on clay, then won the title at Eastbourne on grass.

"She should always play like this, and she would be in the top five, at minimum," Serena said. "It's like, 'Wow, where is this player throughout the rest of the year?'"

That Serena herself was at Wimbledon at all - and in the fourth round, to boot - was a testament to her skill and will.

Days after winning the title at the All England Club in 2010, she cut both feet on glass at a restaurant. She eventually had two operations on her right foot, then was hospitalized for clots in her lungs, then a gathering of blood under the skin of her stomach.

"I think I did really well, just being able to come back and play and win some matches and just really play tough. Even today I lost, but I was able to kind of hang in there," Serena said. "And I can only get better. And that can potentially be really scary, because I can only go up from here."

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