Serbian world No.4 Jelena Jankovic and American second seed Venus Williams entered the quarter-finals of the Bangalore Open in contrasting style.

While top seed Jankovic was clinical in her 6-2 6-2 demolition of Croat Sanda Mamic, world No.7 Williams stumbled past China's Peng Shuai in three sets, committing 15 double faults.

Jankovic, semi-finalist at the Australian Open in January, broke her left-handed opponent in the fifth and seventh games of the opening set after the two had traded early breaks.

The powerful Serbian broke Mamic, who is returning after a career-threatening injury, in the fifth and seventh games of the second set as well to close out the match.

Jankovic will meet China's Yan Zi next.

Former world No.1 Williams was stretched 6-2 6-7 6-2 by her gritty 58th-ranked opponent in a second round match that lasted nearly two hours.

Williams next faces Russian Vera Zvonareva, who beat Romanian qualifier Agnes Szatmari 7-6 6-1.

Williams, a quarter-finalist at the Australian Open in January, had lost to a qualifier in Memphis last week.

With his service letting her down, she looked vulnerable in the first two sets but overcame some early blues to break her opponent in the fifth game of the first set with a powerful forehand.

Gritty Shuai came back strongly in the second, serving hard and returning with precision to trade breaks and win in the tie-breaker before Williams found her groove in the decider.

She and Jankovic join Serena Williams, Swiss Patty Schnyder and Zvonareva as the seeds to have moved into the last eight. Third seed Serena and fourth seed Schnyder booked their berths on Wednesday.

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