Serena Williams' comeback continued with another ruthless display, sweeping past Bethanie Mattek 6-3, 6-1 on Thursday to advance to the quarter-finals of the Cincinnati Open.

Sidelined for six months with an injured left knee, Williams has displayed few signs of rust in her return following up her 6-2, 6-2 first-round victory over second seed Anastasia Myskina on Tuesday with an equally clinical effort against Mattek.

The seven-time Grand Slam winner needed just 63 minutes to dispose of the 105th-ranked American and move into the final eight where she will take on compatriot Amy Frazier.

"Both players I have played so far have been really competitive and really tough," Williams told reporters. "I feel like I'm moving faster but I can still get quicker.

"I feel fine, I've been doing a lot of off court work."

Williams, who has not seen action since the third round of the Australian Open, got the match off to a sluggish start when Mattek broke her to go up 2-1.

But Williams immediately broke then simply overwhelmed Mattek, winning 11 of the next 13 games.

In other second-round action, fifth seed Jelena Jankovic of Serbia eased past Italy's Maria Elena Camerin 6-4 6-4 while sixth seeded Frenchwoman Marion Bartoli battled to a 6-2, 2-6, 6-3 win over Russia's Vasilisa Bardina.

Russia's Vera Zvonareva thrashed Uzbekistan's Lepchenko 6-0, 6-2 to book her spot in the final eight.