PARIS — Roger Federer and Rafael Nadal showed what they can do when challenged.

The two highest-seeded men at the French Open had tougher-than-expected first sets Thursday, and both responded by reeling off game after game to move into the third round.

Although Federer wasn't broken, he lost the first set in a tiebreaker before beating Albert Montanes of Spain 6-7 (5), 6-1, 6-0, 6-4. Nadal faced a close call in the first set, but the three-time defending champion still beat Nicolas Devilder of France 6-4, 6-0, 6-1.

"It was a good test," Federer said.

Seventh-seeded James Blake lost to 19-year-old Ernests Gulbis of Latvia 7-6 (2), 3-6, 7-5, 6-3, and sixth-seeded David Nalbandian was upset by Jeremy Chardy of France 3-6, 4-6, 6-2, 6-1, 6-2.

"I wasn't going for the shots the way I normally do," Blake said.

Venus Williams and Jelena Jankovic reached the third round, one easing through her match and the other playing through pain.

The eighth-seeded Williams used a six-game run to beat 241st-ranked qualifier Selima Sfar of Tunisia 6-2, 6-4. Jankovic, seeded third and a semifinalist at Roland Garros last year, was bothered by a right arm injury but defeated Marina Erakovic of New Zealand 6-2, 7-6 (5).

Amelie Mauresmo, a two-time Grand Slam champion seeded 22nd, lost to Carla Suarez Navarro of Spain 6-3, 6-4.

Nadal improved to 23-0 at the French Open. The second-seeded Spaniard was leading 5-0 in the second set when rain returned to Roland Garros for the fourth time in five days. When they came back on court, Nadal broke Devilder to take a two-set lead and then jumped to another 5-0 lead in the third.

"The second and third sets were very good," Nadal said. "What's really important is that I'm in the third (round) and improving with each match."

Devilder, who broke once in the first set, held his serve in the sixth game of the third set, running the Spaniard all over the court and tapping a volley into an empty space. As the crowd cheered, the Frenchman raised his hands to celebrate.

But six points later, Nadal was into the third round.

Nadal has won the last three French Open titles, defeating Federer in the final the last two years. He is trying to become the first man since Bjorn Borg in 1978-81 to win the clay-court Grand Slam tournament four years in a row.

Federer, a 12-time major champion who still needs to win at Roland Garros to complete a career Grand Slam, was at 5-5 in the first set when the rain interrupted his match.

"The weather conditions were not easy," Federer said. "After (the delay), I felt a bit better, more relaxed.

No. 9 Stanislas Wawrinka, No. 15 Mikhail Youzhny, No. 24 Fernando Gonzalez, No. 26 Jarkko Nieminen and No. 30 Dmitry Tursunov also advanced to the third round.

Mauresmo, who missed the Italian and German Opens because of a rib injury, finished with 38 unforced errors and was broken five times.

"Frankly, I don't know what to say right now, because there was nothing much on my side, apart from a few games in which I was slightly more aggressive and not letting her play that game that much," Mauresmo said. "It's a bit difficult for me to analyze all this. And all I can say is that I feel sorry about the way I played."

Williams trailed 2-1 after being broken early in the first set, but she didn't drop another game until leading 1-0 in the second set. The American made 16 more unforced errors than Sfar, but made up for that with strong play at the net. Williams won the point on 24 of her 35 trips forward.

"It's really nothing planned. I just really feel comfortable at the net, and I don't know why. I just do. I like it up there, so I do try to get there when I can," said Williams, who lost the 2002 French Open final to her younger sister Serena. "It's just finally kicked in. I should always have been there, years ago."

Williams will play No. 26 Flavia Pennetta, who eliminated 16-year-old qualifier Anastasia Pavlyuchenkova of Russia 3-6, 6-1, 6-1.

Jankovic called for a trainer after holding to lead 3-2 in the second set.

"It started gradually, little by little," the Serb told the trainer after grimacing through a massage. "It's humid, and the balls are big and heavy. We're not used to it."

Jankovic refused to bandage her arm.

"I cannot play with tape; just massage it," Jankovic said. "I prefer to play with the pain."

Jankovic broke in the next game to lead 4-2, but Erakovic broke back to 4-3 and held to 4-4. At 5-all, the pair again traded breaks, and the New Zealander led 5-3 in the tiebreaker but Jankovic won the final four points.

No. 7 Elena Dementieva, No. 19 Alize Cornet, No. 27 Katarina Srebotnik, No. 28 Dominika Cibulkova and No. 32 Karin Knapp also advanced, while No. 31 Ai Sugiyama lost.