Venus Williams crashed out of the Wimbledon quarter-finals yesterday while her sister Serena's path to a fourth title became much clearer as she was joined in the semi-finals by three unfancied players.

Second seed Venus, a five-time Wimbledon champion, was knocked out 6-2, 6-3 by Bulgarian world number 82 Tsvetana Pironkova in a shock result.

Defending champion Serena, who is gunning for a fourth Wimbledon singles crown, defeated Chinese ninth seed Li Na 7-5, 6-3 for a semi-final spot.

Venus was not the only big name to take a tumble, as Belgian eighth seed Kim Clijsters, the reigning US Open champion, was downed in three sets by Russia's 21st seed Vera Zvonareva 3-6, 6-4, 6-2.

In the remaining quarter-final, Petra Kvitova of the Czech Republic - who had never won on grass before her run to the last eight here - came from behind to beat Estonian qualifier Kaia Kanepi 4-6, 7-6 (10/8), 8-6.

Serena now faces world number 62 Kvitova in the semi-finals, while Zvonareva takes on Pironkova.

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

The American reckoned her serve was her key weapon this campaign.

"I never serve this well. I always serve well at Wimbledon, but this is the first time I've ever served this well so consistently," the world number one said.

While Serena was rarely troubled, her older sister had a much tougher time of it, losing to the lowest-ranked player in the last eight.

On winning the match, Pironkova fell to the grass in delight, while Venus looked stunned as she trudged off Court One.

"It seems like a dream actually. Coming here I never thought I would play that well and reach that part of the tournament.

I am extremely happy," said Pironkova, who has never made it past the second round here before.

"I think I played pretty well. I'm very happy with my game. She also did well but I have one win over her and actually thought I could win and I was going for it."

This year will be the first time Venus Williams has not been in the final at Wimbledon since 2006. The American has made eight of the last 10 women's singles finals.

In the first quarter-final on Centre Court, Clijsters, the former world number one, won the first set but Zvonareva hit back to take the match.

"It's amazing," the Russian said after her first victory over the Belgian in six attempts.

"I was able to hang in there and play some good tennis out there.

Meanwhile on Court One, Kvitova had to dig deep to see off several match points and recover from 4-0 down in the third set to beat Kanepi.

"I cannot believe it. It's something incredible so I'm very happy," the Czech said.

Aged 20, Kvitova was the youngest player and the only left-hander in the quarter-finals.

"When she broke, she got some more confident and she just kept in there, kept fighting," Kanepi said.

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