It’s a blue Monday for Venus and Serena Williams, who lose in the fourth round at Wimbledon

Down they went, first Serena Williams and then her sister Venus. Between them, the sisters had won nine of the previous 11 Wimbledon championships, yet they were both fourth-round losers Monday.

Serena, the defending champion and a four-time winner here, could never get a handle on the slippery serve of France’s Marion Bartoli or compensate for her lack of match play over the last season. Venus Williams, a five-time champion, was sedately eliminated by Tsvetana Pironkova, the Bulgarian who also knocked her out a year ago.

Bartoli, a 2007 Wimbledon finalist, beat Serena, 6-3, 7-6 (6), and the 29-year-old American who left the All England Club a year ago as a dominating No. 1 leaves this year with her ranking likely to sink to about 175 in the world.

Venus went fairly quietly, 6-2, 6-3. Since her upset of Venus here last year, Pironkova has won only nine matches.

And, just to completely scramble the women’s draw, top-seeded and top-ranked Caroline Wozniacki fumbled away her chance to win her first major title, losing to 5-foot-3 Dominika Cibulkova, 1-6, 7-6 (5), 7-5.

The highest-ranked woman left in the draw is fourth-seeded Victoria Azarenka. The only one who has won a major championship is fifth-seeded Maria Sharapova.

By comparison, the men’s draw stayed sane Monday.

Top-seeded Rafael Nadal took a timeout for a foot injury and later said he was going to have an MRI exam, but the Spaniard withstood the powerful game of 24th-seeded Juan Martin del Potro with a 7-6 (6), 3-6, 7-6 (4), 6-4 win. Next up for Nadal will be the only American left in the singles draws, Mardy Fish.

Fish, seeded 10th, served 23 aces and dominated 2010 finalist and sixth-seeded Tomas Berdych, 7-6 (5), 6-4, 6-4, to reach his first Wimbledon quarterfinal.

Six-time champion Roger Federer, seeded third, had a momentary lapse, playing a sloppy tiebreak, but recovered in plenty of time to beat 18th-seeded Mikhail Youzhny of Russia 6-7 (5), 6-3, 6-3, 6-3. Second-seeded Novak Djokovic dominated 19th-seeded Michael Llodra of France 6-3, 6-3, 6-3.

Bartoli, who lost to Venus Williams in the 2007 final here, appeared to give Serena an opening Monday as she gave up a service break at the end of the second set. She twitched and practiced her service motion in between points, but when it mattered Bartoli collected her nerves and kept Williams off balance.

Serena publicly pronounced herself satisfied with the results in only her second tournament since injuring her foot last July, undergoing two surgeries for that, and recovering from a pulmonary embolism.

“At the end of the day,” she said, “I think I did pretty good.”

She also got feisty when it was suggested that maybe her loss was a good thing for women’s tennis. After all, Serena was asked, wouldn’t her winning after almost a year off have indicated women’s tennis wasn’t very competitive?

“Yeah,” Williams said, “I’m super happy that I lost. Go, women’s tennis.”

Venus seemed puzzled by her thorough beating. “It’s kind of inexplicable why I manage to play some of my worst tennis against [Pironkova],” the 31-year-old said.

This is the first time since 2006 that neither Venus nor Serena will be in the quarterfinals.

Serena, though, said she is optimistic about the rest of the year.

“I think I did really well, just being able to come back and win some matches,” she said. “I can only get better. And that can, potentially, be really scary. I can only go up from here. I can just do so much more.”

diane.pucin@latimes.com

twitter.com/mepucin