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WIMBLEDON, England (AP) — Venus and Serena Williams crossed paths in the locker room at the All England Club, something the sisters often do during the second week of the grass-court Grand Slam tournament.

This meeting came midway through the Wimbledon quarterfinals, and they paused to chat.

Serena was about to play her match. Venus was finished with hers — and it was a loss, a stunning upset against a player ranked 82nd who never before had been past the second round in 18 previous major tournaments.

So much for a fifth all-in-the-family final at Wimbledon.

Five-time Wimbledon champion Venus doubled-faulted five times, made a total of 29 unforced errors and was beaten 6-2, 6-3 Tuesday by Tsvetana Pironkova of Bulgaria, the lowest-ranked woman still in the draw.

"I would have loved to have been around, you know, to come close and hopefully make it an all-Williams final this year," the second-seeded Venus said. "But that won't be."

Over and over, she would shank a shot, then turn toward the Court 1 player guest box where her parents were seated and put her palms up or shrug her shoulders, as if to indicate, "I don't know what's happening here."

"Didn't do myself any favors," the No. 2-seeded Venus said. "I missed all shots today: forehand, volley, backhand. You know, if there was a shot to miss, I think I missed it."

The men's quarterfinals Wednesday are No. 1-seeded Roger Federer vs. No. 12 Tomas Berdych, No. 2 Rafael Nadal vs. No. 6 Robin Soderling, No. 3 Novak Djokovic vs. Yen-hsun Lu, and No. 4 Andy Murray vs. Jo-Wilfried Tsonga. Murray is aiming to become Britain's first male champion at Wimbledon since 1936, while Federer is trying to win a record-tying seventh title at the All England Club.

Venus participated in eight of the past 10 women's finals, losing to her sister three times, including in 2009. She beat Serena for the 2008 title.

Tuesday's match was the older Williams' 77th in singles at the All England Club, and never had she won so few games. The only time she's been beaten at Wimbledon by someone ranked lower than Pironkova was all the way back on June 28, 1997, when the American lost her tournament debut to No. 91 Magdalena Grzybowska.

Really, the only factor preventing this result from truly being considered one of the sport's biggest upsets ever is that Pironkova has done it before: She defeated Williams at the 2006 Australian Open.

Still, even the first woman representing Bulgaria to make it to the final four at a Grand Slam tournament in the 42-year Open era was not anticipating this.

"No one expected me to (reach a) semifinal in Wimbledon," Pironkova said, "and to beat Venus Williams like that."

Surely, Pironkova herself believed this was possible, right?

"If I have to be honest: no," she said. "Coming here, I really just wanted to play a good game, to maybe win one or two rounds. But (a) semifinal looked, to me, very far."

Well, now she's there.

On Thursday, Pironkova will face No. 21 Vera Zvonareva of Russia, who came back to oust No. 8 Kim Clijsters 3-6, 6-4, 6-2. Unlike Pironkova, Zvonareva at least can boast of some experience at this stage, having reached the 2009 Australian Open semifinals.

On the other side of the draw, defending champion Serena Williams smacked 11 aces — lifting her total for the tournament to a Wimbledon-record 73, one more than she hit last year — and made only six unforced errors in a 7-5, 6-3 victory over No. 9 Li Na of China.

"I haven't seen her serve that well in a while," said the Williams sisters' mother, Oracene Price, who joked that "they're stealing some aces from Serena; we're counting."

Serena's match on Centre Court began after Venus' loss was over, so the two most successful siblings in tennis history ran into each other.

One was getting set to compete. The other was done for the day — and the tournament, at least in singles. The sisters are scheduled to appear in the doubles quarterfinals Wednesday.

"I don't know if it affected my play too much," Serena said. "I just had to keep playing and focusing."

She next faces yet another unheralded member of this year's final four, 62nd-ranked Petra Kvitova of the Czech Republic, who saved five match points and erased third-set deficits of 4-0 and 5-2 to eliminate 80th-ranked qualifier Kaia Kanepi of Estonia 4-6, 7-6 (8), 8-6.

"I play now very well, my best tennis in my life, my career," said the left-handed Kvitova, who knocked off No. 3 Caroline Wozniacki, No. 14 Victoria Azarenka and No. 23 Zheng Jie en route to her first Grand Slam quarterfinal.

Asked if she thinks she can win the title, the 20-year-old Kvitova, who wears braces on her teeth, replied: "I don't think so. No."

Perhaps that's because she hadn't won a grass-court match until last week.

Pironkova (her first name is pronounced sve-TAH-nuh, her last pee-RON-ko-vuh) and Kvitova (keh-VIT-oh-vuh) give Wimbledon two unseeded women in the semifinals for the first time since 1999. Indeed, Serena Williams is the only remaining woman with a Grand Slam championship; she owns 12.

"It's not mine to lose; it's mine to win, if I can get it," the three-time Wimbledon champion said. "There's three other people that are vying to win it. They have just as good a chance as I do."