Top seed Serena Williams rediscovered her best form to trounce Aranxta Parra Santonja 6-0, 6-3 and move into the quarter-finals of the JP Morgan Chase Open in Carson, California on Thursday.

Serena was joined in the last eight by her sister and second seed Venus, who crushed Elena Likhovtseva 6-1, 6-1 on a day when seven of the top eight ranked players in the event advanced.

Unhappy with her sloppy performance in her second round victory over Elena Daniilidou, Serena tightened her game against the Spaniard, who had a tough time trying to keep up with the American's blistering pace.

Serena raced through the first nine games of the match before Parra Santonja began to vary the speed and direction of her shots and fought back to even the second set at 3-3.

However, the number one seed moved further inside the court and bludgeoned her way to victory with some brutal groundstrokes.

"I got into the groove and was a lot more comfortable. She changed up her game and I had to adjust," Serena said.

Serena next lines up against eighth seed Vera Zvonareva of Russia, a 6-2, 6-3 winner over France's Marion Bartoli.

Venus will take on eleventh seed Francesca Schiavone, who caused the only upset of the round when she edged out Japanese sixth seed Ai Sugiyama, 6-3, 0-6, 7-6.

Third-seeded American Lindsay Davenport also had an easy day with a 6-2, 6-4 victory over 15th-seeded compatriot Amy Frazier.

Davenport, who won in Stanford last week, will face number seven seed Nadia Petrova after the Russian eased past Jelena Kostanic 6-3, 6-2.

Fourth seed Elena Dementieva fought off two set points to defeat 14th-seeded Chanda Rubin 7-5, 7-6 to earn a quarter-final match against fifth seed Svetlana Kuznetsova, a 6-3, 6-0 winner over Israel's Anna Smashnova-Pistolesi.

French Open finalist Dementieva was pleased with her battling performance.

"It was difficult because we've played so many times in the last year and I've always won," Dementieva said.

"I realise how much she wants to beat me. Every time I play against Chanda, I know I have to be focused because she is very motivated against me."