Pironkova, ranked No. 82 by the WTA Tour, beat the American No. 2 seed and last year’s runner-up, 6-2, 6-3, on Court 1. Defending champion Serena Williams beat Li Na of China in straight sets, while Vera Zvonareva of Russia defeated eighth- seeded Kim Clijsters of Belgium.
“I have received quite a few phone calls” from Bulgaria, Pironkova said in a news conference. “Everyone was so happy and excited. Honestly, I think no one expected me to play a semifinal in Wimbledon and to beat Venus Williams like that.”
She said there are no journalists from Bulgaria covering the event at the All England Club in London.
At least one of the Williams sisters has reached the final in nine of the 10 years since Venus’s first title at the championships in 2000.
Serena Williams will face unseeded Petra Kvitova of the Czech Republic in the semifinals as the top seed bids for her 13th Grand Slam title. Kvitova, who never before had been beyond the fourth round of a major, beat Kaia Kanepi, a qualifier from Estonia, 4-6, 7-6 (10-8), 8-6.
Venus Williams made 29 unforced errors against Pironkova, who made only six. The American had made 50 unforced errors in her four previous rounds, all won in straight sets, an average of 12.5 per match.
Williams also struggled with her serve, normally one of the best parts of her game. She had three aces and a winning percentage of 58 whenever her first serve landed in. Pironkova, who also had three aces, was successful on her first serve 74 percent of the time.
Pironkova, aiming for her first career title, broke Williams’s serve for 4-2 in the opening set, which she wrapped up with a backhand passing shot, once again breaking the American’s serve.
She continued to dictate the rallies against the five-time champion in the second set.
Williams, who lost last year’s final to her sister Serena, broke for 2-1. Pironkova fought back in the next game, reaching two breakpoints with a backhand lob over the 6-foot-1 American. She broke back for 2-2 as Williams hit a forehand low into the net. The American also dropped her next service game, with a backhand error.
Serving to stay in the match at 5-2 down, Williams overcame two match points. She saved the first one as Pironkova hit a backhand into the net. The second match point was fended off with a forehand winner.
Serving to become the first Bulgarian woman in a major semifinal, Pironkova won on her third match point as Williams hit a forehand volley wide.
Pironkova had only one win on the London grass courts before this year, and had beaten Williams once before, in the first round of the 2006 Australian Open. Williams took their only other encounter before today, in Istanbul in 2005.
“I just didn’t get enough balls in today,” Williams said in a news conference. “Just let it spiral and didn’t get any balls in. I had a lot of opportunities and a lot of short balls. I just seemed to hit each one out.”
It is Williams’s earliest Wimbledon exit since 2006 and denies the 30-year-old of what would have been her 200th victory at a Grand Slam. It was the 13th win at a major for Pironkova, the first against a top-two player.
Serena Williams, also the Wimbledon champion in 2002 and 2003, beat Li 7-5, 6-3 on Centre Court.
The 28-year-old American, who secured her 12th Grand Slam title at this year’s Australian Open, broke in the 11th game of first set after coming back from 0-40. Li hit a forehand into the net, then a forehand long, before a double-fault made it 40- 40. Another double-fault and an overhit volley gave the game to Williams, who then served out the set.
Williams broke twice in succession for 5-2 in the second set, with a double-fault again contributing to the second, but Li broke straight back. The Chinese player was again unable to hold in the next game, giving her opponent the match.
“I didn’t have a good practice today, so I was a little nervous,” Williams told the British Broadcasting Corp. “But I can’t believe I am in the semis, I am very excited.”
Clijsters, playing at Wimbledon for the first time since 2006 after returning from a two-year retirement, was denied her third semifinal appearance after the 21st-ranked Zvonareva beat her for a first time, 3-6, 6-4, 6-2.
Clijsters, who won the U.S. Open last year as a wild-card entrant shortly after returning to the tour, took the first set as her opponent hit a backhand return long.
Zvonareva, 25, a semifinalist at the 2009 Australian Open, broke for a 3-1 lead in the second set, then Clijsters broke back in the ninth game to give her the chance of taking it into a tiebreak.
Instead, Zvonareva broke back immediately and clinched the match on a double-fault by the 27-year-old Clijsters.
“I’m disappointed,” Clijsters said in a news conference. “It’s too bad I wasn’t able to come up with my best at the important time in the match. She did. She was very consistent, didn’t give me any easy mistakes. I gave her a few too many.”
Clijsters had 36 unforced errors and produced two aces, while Zvonareva made 19 mistakes and had three aces.
Zvonareva, who plays Pironkova in the next round, said reaching the semifinals was “definitely one of my dreams.”