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."

Video Highlights: Serena shocked by Bartoli Take a look at how defending champion Serena Williams was knocked out in straight sets by Marion Bartoli in the fourth round. NBCSports.com

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.

They won't be around for the women's quarterfinals Tuesday, 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.

Video Bartoli stayed focused, mentally tough in win over Serena Marion Bartoli says she's proud that she held off defending champion Serena Williams in the fourth round. NBCSports.com

Sharapova is the only quarterfinalist who's won a Grand Slam title; her three major championships include Wimbledon in 2004.

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.