Clijsters rolls on as Williams sisters tumble

Kim Clijsters kept her comeback rolling, but America's Williams sisters fell by the wayside at the two million-dollar WTA tournamen here on Thursday.

Former world number one Clijsters, playing her first tournament in two years, booked a quarter-final berth with a 6-4, 4-6, 6-2 victory over sixth-seeded French Open champion Svetlana Kuznetsova.

The Belgian will play either top seeded Russian Dinara Safina or China's Peng Shuai in the quarters.

But as Clijsters' dream return to the courts continued, the day proved a nightmare for both Serena and Venus Williams.

Second-seeded Serena, the reigning US Open, Australian Open and Wimbledon champion, was stunned by 29th-ranked Austrian Sybille Bammer 7-5, 6-4.

Bammer broke the error-prone Serena three times en route to the victory.

Red-hot Italian Flavia Penetta, fresh from victory in Los Angeles on Sunday, toppled third-seeded Venus Williams 7-6 (7/2), 6-4.

"I'm shaking," said the Italian, adding that such emotion was "very unusual" for her.

"Coming from Los Angeles, I didn't have many days to rest. I was playing like that yesterday, not my best tennis. I was tired. When everything comes together, the emotions go up."

Nothing was coming together for Venus, whose 38 unforced errors included untimely forehands long in the first-set tiebreaker and a forehand over the baseline on match point.

"I wasn't able to get control of my ball today," Williams said. "After a while, it was obvious to see she was just keeping the ball in play and waiting for me to self-destruct."

Pennetta will play Slovakian Daniela Hantuchova, who advanced with a 7-6 (8/6), 0-6, 7-6 (7/5) victory over seventh-seeded Vera Zvonareva of Russia.

Fourth-seeded Russian Elena Dementieva, who nabbed Olympic gold in Beijing last year, beat Romanian Sorana Cirstea 6-4, 6-4 to set-up a quarterfinal with rising Danish star Caroline Wozniacki.

Wozniacki the eighth seed, advanced as Hungary's Melinda Czink retired injured while trailing 3-0 in the opening set.