Williams, an eight-time Grand Slam champion who is trying to win her second title at Roland Garros, took a 4-0 lead in the first set, but struggled at times in the second.

Roger Federer also advanced to the quarterfinals, beating No. 13 Mikhail Youzhny of Russia 7-6 (3), 6-4, 6-4. The top-ranked Swiss star tied the Open-era record for most consecutive sets won at Grand Slams, taking his streak to 35.

"I've got enough shirts for five-set matches in the bag," Federer said. "I only used one today."

Federer next faces No. 9 Tommy Robredo, who defeated No. 29 Filippo Volandri of Italy 6-2, 7-5, 6-1. Federer beat Robredo at the Australian Open.

Federer, trying to win his fourth consecutive major title and complete a career Grand Slam, also matched another Grand Slam mark with 11 straight-set victories in a row. John McEnroe set both records during Wimbledon and the U.S. Open in 1984.

Federer hasn't lost a set at a major tournament since dropping the second set of last year's U.S. Open final against Andy Roddick. He won the last two sets of that match, then won all seven of his matches at the Australian Open in January in straight sets — becoming the first man to win a Grand Slam title without dropping a set since Bjorn Borg at the 1980 French Open.

"Maybe if I win first set, it would be something different," Youzhny said.

The 10th-seeded Safina broke Williams at love to even the second set at 3-3, but the American then won 12 of the last 14 points.

"That was definitely better today," said Williams, who missed the last two French Opens with injury but won the Australian Open in January.

Safina hurt herself with five double-faults, but her powerful groundstrokes keep Williams moving all over the court.

"She hit hard, then she hit lobs, then she hit soft balls," Williams said. "She really gave me a lot of different pace."

Henin, who is trying to win her third French Open title, beat No. 20 Sybille Bammer 6-2, 6-4.

"I know she's playing great, but I never count myself out," said Williams, who lost to Henin in a contentious 2003 French Open semifinal match.

Williams has won both of their matches since, including the final at Key Biscayne, Florida, in March.

"I will just have to be focused on my goal," Henin said. "I want to win this match and I will give eveything I can."

Third-seeded Svetlana Kuznetsova advanced by beating No. 15 Shahar Peer of Israel 6-4, 6-3, and No. 6 Nicole Vaidisova reached the quarterfinals by defeating No. 19 Tathiana Garbin of Italy 6-3, 6-1.

"I feel like I'm getting better on clay," said Vaidisova, who reached the semifinals at Roland Garros last year and also made the last four at this year's Australian Open. "For some people it's a tough surface, but I like playing on it."

In the quarterfinals, Vaidisova will face No. 4 Jelena Jankovic, who beat Marion Bartoli of France 6-1, 6-1. Seventh-seeded Ana Ivanovic also advanced, beating No. 24 Anabel Medina Garrigues of Spain 6-3, 3-6, 6-3, and will next play Kuznetsova.

On the men's side, Guillermo Canas defeated Juan Monaco 6-0, 6-4, 6-2. Canas, who beat Federer twice this year, could meet the 10-time Grand Slam champion in the semifinals.