Venus Williams stunned in Wimbledon quarterfinals
The second-seeded Williams, who had reached the Wimbledon final in eight of the past 10 years, was undone by a slew of unforced errors and double faults in the biggest upset of the women's tournament. It was Williams' worst loss at Wimbledon in terms of games won — only five.
In another surprise, 21st-seeded Vera Zvonareva of Russia rallied to beat two-time U.S. Open winner Kim Clijsters 3-6, 6-4, 6-2 to reach her first Wimbledon semifinal.
Williams never got going against the 22-year-old Pironkova, who is the lowest-ranked player remaining in the women's draw and had never previously passed the second round in 18 previous Grand Slam appearances.
"I just didn't get enough balls in today," said Williams. "I let it spiral and didn't get any balls in. I had a lot of opportunities, a lot of short balls and I seemed to hit each one out.
"If there was a shot to miss, I think I missed it. ... I didn't bring my best tennis today."
The loss rules out another all-sister final between Venus and Serena Williams, the defending champion who faced China's Li Na in a later quarterfinal.
Pironkova beat Venus Williams in the first round of the Australian Open in 2006, but few gave her a chance of replicating the feat on the grass of Wimbledon, where Williams has dominated for a decade.
But Williams was clearly off her game, committing 29 unforced errors compared to just six for Pironkova. Williams had five double-faults, including back-to-back doubles in two games.
She also hadn't lost at a Grand Slam to a player outside the top 80 since that defeat in Australia to Pironkova, then ranked No. 143.
"Honestly, I think no one expected me to play semifinal in Wimbledon and to beat Venus Williams like that," Pironkova said. "Coming here I really just wanted to play a good game, to maybe win one or two rounds.
"I still cannot believe that I reached the semifinals. This is truly like a dream to me."
Pironkova denied Williams her 200th career win on grass and spoiled the prospect of a fifth Wimbledon final against Serena, who beat her older sister last year for her third title at the All England Club.
Pironkova becomes the first woman representing Bulgaria to reach a Grand Slam semifinal in the Open era. Bulgarian-born Manuela Maleeva-Fragniere was representing Switzerland when she reached the U.S. Open semifinals in 1992 and 1993.
Pironkova broke Williams twice in the first set, winning four straight games after a 2-2 tie, then finished the set with a backhand passing shot down the line.
After Williams broke to go up 2-1 in the second set, it looked as though she might be able to take command. But Pironkova broke right back in the next game, which included the shot of the match. After Williams hit a forehand drop volley, the Bulgarian raced forward and flipped a backhand lob winner over Williams' head. Pironkova swung her arm in an uppercut celebration.
Down 5-2, Williams saved two match points, but Pironkova served out the match in the next game. After Williams missed a forehand volley, Pironkova squealed and fell on her back on the turf.
Pironkova earned a semifinal berth against Zvonareva, who rallied for her first win over Clijsters in six meetings.
Clijsters, returning to Wimbledon for the first time since 2006 after coming out of retirement, beat fellow Belgian Justine Henin on Monday and was viewed as a potential title threat.
The eighth-seeded Clijsters looked in command after sailing through the first set, but the match turned in the Russian's favor after she broke to go up 3-1 in the second.
Clijsters finished with 36 unforced errors, compared to 19 for Zvonareva.
"It's too bad I wasn't able to come up with my best at the important time in the match," Clijsters said. "She did. She was very consistent, didn't give me any easy mistakes. I gave her a few too many."
In another quarterfinal, unseeded Petra Kvitova of the Czech Republic played qualifier Kaia Kanepi of Estonia.
The men had the day off ahead of Wednesday's quarterfinals.