THERE WERE four quarter-finals played yesterday but only two names hung on the lips: Venus and Serena. The Williams sisters have perennially defied tennis logic; they came from the wrong side of the tracks, developed their muscles more than anyone else and learned the game from tapes and books bought by their gently eccentric father, Richard.

They have dipped into the professional tour as they have seen fit, using it for their own particular purpose of winning Grand Slams, and have been criticised for doing it their own way for over eight years.

The Williamses have broken with convention, changed the game and this year arrived at Wimbledon without having played or practised on grass. They had played in only seven tournaments since the season began and now Venus is hitting her serves as hard as the men.

"How did you practise for Wimbledon?" Serena was asked after her first-round match.

"Hard court in Florida," she said without a hint of irony.

Not sharp enough on grass and apathetic about tennis was the general opinion of the sisters before the tournament began and the top four seeds startled and froze themselves out of the running.

As the elite players continue to compete on a marathon hike across continents for 10 months without a break and continue to play when they are injured, all of a sudden the Williamses' tried and trusted method of minding their bodies is gaining a following.

This unfailingly extraordinary duo have lifted the Wimbledon title six times this century, and yesterday they punched their way closer to a third all-Williams final, having played each other in the 2002 and 2003 deciders.

Serena, playing perhaps her strongest match yet, swept aside Agnieszka Radwanska, 6-4, 6-0, in less than an hour. Venus beat Tamarine Tanasugarn 6-4, 6-3 but ended the match limping.

Elena Dementieva almost had a sensational collapse against her compatriot Nadia Petrova but untangled her thoughts enough to pull out of a third-set tailspin.

Dementieva has had such turns before, the most destructive of which was the 2004 Roland Garros final, where she disintegrated against Anastasia Myskina, 6-1, 6-2. Having won the first set 6-1 yesterday, Dementieva led the second 5-1, stood up to serve for the match and ended up losing the set on a tiebreak amid a storm of serving errors.

"I just somehow lost my concentration again," she explained.

The fairytale matinee also kept running to a full house when Jie Zheng's busy, all-court game continued to knock over the bigger names. Yesterday it was 18th seed, Nicole Vaidisova, who tumbled just as the world number one, Ana Ivanovic, had done before her. And what a fall.

The Czech teenager, standing head and shoulders above the wild card from China, went out in three sets, conceding the first 6-2, fighting back to edge the second 5-7 before collapsing to an ignominious 6-1 exit.

It leaves the semi-final line-up looking semi-familiar. Venus faces Dementieva and Serena plays Zheng for a place in the final.

"I'm fine. I'm walking around on two legs, doing good, so I'm not really concerned right now," said Venus about her leg.

"I mean there's really nothing happening. It's just regular maintenance and I think I'll be fine for the doubles. I promise I'm fine.

"Thank you for your concern, you guys."

The serve was her big weapon; every time Tanasugarn seemed to get a foothold in a game, Williams would turn it back her way with a delivery. The Thai had eight break points and converted one of them in the first set, while Williams earned five and took two in 56 minutes. The second set again gave Tanasugarn opportunities but again Williams broke twice and her opponent once.

"Her game and her style is really hard because she had a very, very hard weapon, you know, big serve and big groundstrokes" said Tanasugarn. "She served very well, acing me many times. I was like, next life can I be as tall as her please?"

In the second set Williams won all of the points on her successful first serves.

Serena was more brutally dominant with Poland's Radwanska, winning by 6-4 and a crushing 6-0.

"I surely hope so," she said when asked if she thought a Williams name would be on the trophy again."

And her opponent Zheng?

"I think she's doing a fabulous job and I don't think it's luck. I think she's a very good player."

The Chinese later said she would give all her prize money to the Sichuan earthquake fund,

Zheng comes from the Sichuan province in southwest China, where an estimated 60,000 were killed and five million made homeless in May.

Beating Serena in the semi-final would bring her donation to €474,000, a defeat would mean €237,000.

"I will donate all my portion. After going back after Wimbledon I will do more charity work and encourage more people to come and support the stricken region," said Zheng.

"I will do as much as I can to help the Sichuan people because that is where I come from."