STUTTGART, Germany — Venus Williams reached the Porsche Grand Prix quarterfinals, defeating Ukraine's Kateryna Bondarenko 6-4, 6-2 today one day after sister Serena was beaten and lost her No. 1 ranking.

Williams, seeded sixth, served 12 aces and won in 66 minutes. She fell behind 3-1 but recovered to break serve twice in taking the first set.

"She played really well," Williams said. "She had an early break and I needed to break her back. I felt comfortable on the court."

Williams, the Wimbledon champion, was joined in the quarterfinals by three Russians — Dinara Safina, Vera Zvonareva and Nadia Petrova. Jelena Jankovic played Bondarenko's older sister, Alona, in the last second-round match.

Safina seeded third, rallied in the second set to beat Bulgarian qualifier Tsvetana Pironkova 6-1, 7-6 (6) and will next play Williams. Zvonareva, seeded seventh, spoiled Marion Bartoli's 24th birthday by beating the Frenchwoman 6-2, 6-0, while Petrova overcame Patty Schnyder of Switzerland 6-4, 6-1.

"I didn't give her a chance to get into the match," said Zvonareva, the Olympic bronze medalist. "I played pretty well and consistent."

Petrova, the 2006 champion in Stuttgart, will meet Li Na in the quarters. Zvonareva will face Jankovic or Alona Bondarenko.

Safina has a chance at finishing the year at No. 1 after a breakthrough season during which she has won four titles. She also was runner-up at the French Open and Olympics and a U.S. Open semifinalist.

"I didn't play at my best. I was going for my shots even if I was missing some," Safina said.

Jankovic will be the new No. 1 in Monday's rankings. The Serb was assured the top spot when Serena Williams lost to Li on Wednesday. Jankovic was No. 1 for a week in August.

Since Justine Henin retired in May, four players have been No. 1: Ana Ivanovic, Jankovic, Maria Sharapova and Serena Williams.

Ivanovic and Sharapova are the only top-10 players who did not come to Stuttgart.