Nadal improved to 28 wins from 32 career matches at Indian Wells, where he's won twice. The world's top-ranked men's player has lost six games in his first two matches while showing no lingering effects from his recent left thigh injury.

"I didn't play nothing really impressive, but I played solid. I didn't have big mistakes," he said. "The more positive thing is I finished much better than the beginning of the match. So improve during the match always very good news, no?" Women's top seed Caroline Wozniacki of Denmark advanced with a 6-1, 6-3 victory against Maria Jose Martinez Sanchez of Spain that took just over an hour. Wozniacki has improved her results in each of her first four years playing at Indian Wells, where she was runner-up to champion Jelena Jankovic last year.

"It was important to move my feet, try to get as many returns back, and it helped me a little bit that she didn't get too many first serves in so I could go in and dictate the game," Wozniacki said. "As long as I kept her on the baseline, then I felt like I was in control of the point.

It was very important to keep the pressure but not force it too much." Russian Dinara Safina defeated No. 4 seed Samantha Stosur of Australia 7-6 (2), 6-4 in the lone upset on the women's side. Stosur reached the semifinals here last year. Former world No. 1 Safina is making a comeback after being sidelined with a back injury last year.

American Sam Querrey beat Spaniard Fernando Verdasco 7-5, 6-4.

Other women's winners were No. 8 Victoria Azarenka of Belarus, No. 9 Agnieszka Radwanska of Poland, No. 16 Maria Sharapova and No. 22 Alisa Kleybanova of Russia.

Sharapova beat 20th-seeded Aravene Rezai of France, 6-2, 6-2 as the Russian star returns to the WTA Tour after a five-week absence because of illness.

"I started like I didn't have my cup of coffee or something, didn't have my peeps around, so that was disappointing," Sharapova said. "When she's on, she can be one of the toughest players to play against. She had a lot of errors. I returned a lot better, and served a lot better in the second set." Petrova needed more than two hours to derail the upset hopes American wild card Christina McHale, who lost 3-6, 6-4, 6-2 when the Russian sent a backhand down the line on match point.

There were two upsets on the men's side: fourth-seeded Robin Soderling of Sweden and No. 11 seed Nicolas Almagro of Spain both lost.

Soderling fell to No. 32 seed Philipp Kohlschreiber of Germany, 7-6 (8), 6-4 after holding five set points in the tiebreaker; while 23rd-seeded Albert Montanes of Spain took out Almagro 4-6, 6-2, 6-4.

Soderling was bothered by a left foot injury that first occurred during Sweden's victory over Russia in Davis Cup play nearly 10 days ago.

"I lost the match when I decided to go on court," he said. "I shouldn't have done that. It's pretty stupid to play." Soderling, who was in bed for five days with a fever before the tournament began, had yet to have his foot examined by a doctor. He is scheduled to play at Key Biscayne, Florida next week.

"Hopefully, they won't find anything bad," he said.

"The more I play on the foot, the worse it gets." American qualifier Donald Young's run ended with a 6-0, 6-4 loss to 25th-seeded Tommy Robredo of Spain. Young upset fifth-ranked Andy Murray two days ago.

Juan Martin del Potro of Argentina, the 2009 U.S. Open champion, defeated 20th-seeded Alexandr Dolgopolov of Ukraine 7-6 (3), 6-3. Qualifier Somdev Devvarman of India outlasted Xavier Malisse 6-1, 3-6, 7-6 (5).

Nadal delayed the start of his post-match interview to watch the tiebreaker since he will play Devvarman in the fourth round.