Qualifier Jelena Dokic upset fifth-seeded Nadia Petrova 6-4, 7-6 (4) in the second round of the Open Gaz de France on Thursday, setting up a quarterfinal against Australian Open champion Kim Clijsters with the No. 1 ranking on the line.

At the start of the first set, Dokic forced Petrova to save three break points. In the 10th game, Petrova trailed 0-40 on serve and saved one set point before sailing a forehand long.

Dokic sealed the win in the tiebreaker when she forced Petrova back with a powerful return, and the Russian hit a forehand into the net.

The 120th-ranked Dokic will face four-time Grand Slam champion Clijsters for the first time in eight years. Clijsters leads the series 6-3, but Dokic won their last match in 2003.

If Clijsters wins Friday and reaches the semifinals, she will overtake Caroline Wozniacki at the top of the rankings. The Belgian last held No. 1 in January 2006.

The careers of Dokic and Clijsters have gone in opposite directions since they teamed up to win the 1998 French Open junior doubles title. Dokic is excited about the challenge.

"It's the toughest match you can play, it's a great test," Dokic said. "I think she really is the number one player in the world. She's won (the) U.S. Open and Australian Open, a Masters as well. I'm really looking forward to the match, as I have nothing to lose.

"I think we play a little bit similar, we play pretty aggressive."

In other second-round matches, third-seeded Kaia Kanepi of Estonia beat Sofia Arvidsson of Sweden 6-3, 6-4; fourth-seeded Petra Kvitova of the Czech Republic needed five match points to beat Barbora Zahlavova Strycova 6-4, 6-7 (6), 7-6 (9). Kvitova converted only four of 19 break-point chances in a match lasting 3 hours, 15 minutes.

Kvitova will play No. 7 Yanina Wickmayer of Belgium in the quarterfinals. Wickmayer needed less than an hour to defeat Klara Zakopalova of the Czech Republic 6-1, 6-3.

Earlier, Maria Sharapova withdrew before her match against Bethanie Mattek-Sands of the United States because of illness. Mattek-Sands edged Stephanie Cohen-Aloro of France 7-5, 6-3 and faces No. 6 Andrea Petkovic of Germany, who rallied from 3-0 down in the first set to beat Kristina Kucova of Slovakia 6-4, 6-2.

In Friday's other quarterfinal, Kanepi will face No. 8 Dominika Cibulkova of Slovakia.