Williams sisters remain on collision course

Serena Williams believes more big serving can carry her to consecutive Wimbledon triumphs after she saw off a spirited fourth-round challenge from Maria Sharapova.

The defending champion and sister Venus survived faced stiff tests as they successfully reached the quarter-finals today, while fellow top-four seeds Caroline Wozniacki and Jelena Jankovic crashed out.

While both Williams sisters had to come through tie-breaks, the only fourth-round contest to go to three sets was, unsurprisingly, the all-Belgian affair on Court One with Kim Clijsters edging past Justine Henin.

The top seed faced three set points in her opener against former world number one Sharapova, who beat her in the 2004 final, but came back to win 11-9 on the tie-break and then secured a 6-4 second-set victory.

‘I served really well,’ Williams said. ‘I had a little bit of a hiccup, but she returned really well. It forced me to serve really well.

‘It was just hard to get a rhythm out there. She served really well.

‘But I hope if I serve like this, at least I won't drop serve. I don't serve like this too often.

‘I don't know what it is about this court that makes me serve.’

Sister Venus was also complimentary about her opponent after beating unseeded Australian Jarmila Groth 6-4 7-6.

The five-times champion twice came back from breaks in the second set to secure a quarter-final against Bulgarian Tsvetana Pironkova, who beat 11th seed Marion Bartoli 6-4 6-4.

She said: ‘We were both serving very well, so that definitely made it close.

‘There wasn't a lot of room for error for either one of us against each other's serve.

‘She just played really well. I didn't think she made too many errors.

‘She just really played some smart tennis and took advantage of her opportunities. I thought I played well at the end to close it out.’

Third seed Wozniacki was dumped out 6-2 6-0 by Petra Kvitova, who is ranked 62nd in the world, to ensure there will be an unseeded semi-finalist.

The 20-year-old Czech, who revealed after her shock victory that she had been working hard on her serve, will face world number 80 Kaia Kanepi following the Estonian's 6-2 6-4 triumph over Klara Zakopalova.

Clijsters recovered from a poor start to dominate the second set against Henin, who suffered an elbow injury in a heavy fall early in the contest, and retained her edge to win 2-6 6-2 6-3.

The 27-year-old lost to Henin in the last four on her previous Wimbledon appearance in 2006 but she now feels more confident on grass.

The US Open champion said: ‘I've always had a lot of respect and admired Wimbledon as a tournament.

‘But in the past, I've never had that same comfortable feeling out there as I did on hard court in America or the US Open.

‘Since I've come back, I definitely feel a lot more comfortable moving from side to side. Those first few steps are really important - I'm a lot more in control of those.’

Clijsters will take on 21st seed Vera Zvonareva after Jankovic pulled out of their match with a back injury as the Russian led 6-1 3-0.

Ninth seed Li Na will face Serena Williams in the last eight after the Chinese player claimed a 6-3 6-2 victory over seventh seed Agnieszka Radwanska of Poland.