Serena Williams took the first step toward winning a third consecutive tournament when she beat Lucie Hradecka of the Czech Republic 6-3, 7-6 (5) in the first round of the Western & Southern Open on Tuesday in Mason, Ohio.

China's Li Na beat Lucie Safarova 6-3, 6-4 to become the first woman to reach the third round. The win was Li's first since losing in the second round at Wimbledon. She lost in the first round last week in Toronto.

"I needed some matches for the hard court," said Li, who won the French Open in June and reached the Australian Open finals in January. "It's always tough, but I was happy I could win the match today."

Williams, who last won three straight tournaments at the beginning of the 2008 season, has improved her world ranking from No. 175 to No. 31 in her comeback from injury and illness. She has won 12 straight matches, equaling Kim Clijsters and Victoria Azarenka for the longest such streak on the WTA Tour this year.

Federer wins

Defending men's champion Roger Federer reached the third round with a 6-3, 7-5 win over Argentina's Juan Martin Del Potro, who had won the last two matches between the pair, including the 2009 US Open final.

"I expected a tougher match, for obvious reasons," Federer said. "It went better than I thought. I had a wonderful first set, and the second set, too. I was able to keep him from playing the game he likes to play."

Fourth-seeded Maria Sharapova, sixth-seeded Petra Kvitova and No. 8 Marion Bartoli all cruised into the third round. Sharapova beat Australia's Anastasia Rodionova 6-1, 6-3, Kvitova advanced with a 7-6 (3), 6-3 victory over South African Chanelle Scheepers, and Bartoli posted a 6-1, 6-2 win over Ukrainian Alona Bondarenko.

Jelena Jankovic, seeded 13th, advanced to the second round with a 6-0, 6-3 romp over Iveta Benesova.

Flavia Pennetta upset 12th-seeded Anastasia Pavlyuchenkova 2-6, 6-3, 6-3, and 16th-seeded Peng Shuai of China and No. 17 seed Yanina Wickmayer of Belgium also advanced.

In the men's draw, Michael Llodra upset 13th-seeded Mikhail Youzhny 7-5, 3-6, 7-6 (4).

Eight-seeded Tomas Berdych defeated Juan Monaco 7-6 (2), 6-0. Ninth-seeded Nicolas Almagro, 10th-seeded Gilles Simon and No. 15 seed Jo-Wilfried Tsonga also moved on.