By Chris Bevan BBC Sport at Wimbledon

Venus and Serena have won six of the last eight Wimbledon titles

The Williams sisters are favourites to win their quarter-finals at Wimbledon on Tuesday as they seek to set up a potential meeting in the final.

Between them, defending champion Venus and younger sister Serena, have won six of the last eight singles titles here.

Venus takes on Thailand's Tamarine Tanasugarn, who shocked second seed Jelena Jankovic in the fourth round.

Serena is up against Polish teenager Agnieszka Radwanska, who overcame fourth seed Svetlana Kuznetsova.

The other matches see fifth seed Elena Dementieva meet Nadia Petrova in an all-Russia clash and wildcard Jie Zheng play Nicole Vaidisova.

None of the top four women's seeds, Ana Ivanovic, Jankovic, Maria Sharapova and Kuznetsova made the last eight - the first time that has happened since seedings were introduced at Wimbledon in 1927.

It has been a tournament full of shocks, leaving the draw wide open for Serena and Venus, seeded sixth and seventh, to come through relatively unchallenged.

Venus, who has beaten Tanasugarn in each of their six previous meetings, will be expected to continue her progress as she chases her fifth title.

606: DEBATE Vaidisova and Venus will win but if Petrova is fully fit she will beat the mentally weak Dementieva kuzfan

Tanasugarn, at 31 the oldest woman left in the competition and into her first Grand Slam quarter-final, admits the odds are stacked against her but is adamant she will enjoy herself.

"I have played her many times and she has kicked my backside," Tanasugarn said. "So I am just happy to be in the quarter-finals and there is no pressure at all for me.

"If I win it will be a great feeling but I will just go out there and have fun and do my best."

Venus has not even dropped a set in the past against Tanasugarn and says she knows what to expect from the Thai.

"Obviously she's playing well here," Venus said. "She's just marched through to the quarter-finals.

"I have not seen her play this year but I have played her a number of times. I think I'll be more prepared as far as knowing how she plays than with my first four opponents. That makes it a little bit easier."

Radwanska, 19, who won the Eastbourne tournament in the build-up to Wimbledon, believes she has a chance against Serena on grass.

I have played Vaidisova maybe two or three times and I have never won once one. I don't want to think too much - I will just be trying my best Jie Zheng

"First of all, you know, I have to play a very good match to beat her," the 14th seed said. "I played once against her in Berlin on clay.

"But now is on grass, so I don't know. I will see. I just like the surface though."

Petrova, who beat Sharapova's conqueror Alla Kudryavtseva 6-1 6-4, fancies another upset against Dementieva, who is the highest-seeded player left in the draw.

"I've realised I really have a good draw to be in the quarters," Petrova said. "All I need to do is just stay there, have my head focused and play the right tactics, play a smart game."

Zheng, who is also into her first quarter-final, must overcome 18th seed Vaidisova of the Czech Republic.

The Chinese world number 133 beat Agnes Szavay 6-3 6-4, and said: "I feel I just played so well.

"I have played Vaidisova maybe two or three times and I have never won once one. I don't want to think too much. I will just be trying my best."