CINCINNATI: Second-seeded Serena Williams cruised into the third round of the two million-dollar WTA Tour event here Wednesday as Belgian Kim Clijsters kept her comeback on track with a straight sets victory.

Reigning US Open, Australian Open and Wimbledon champion Williams needed little more than an hour to dispatch Kateryna Bondarenko, 6-3, 6-2, firing 13 aces past the unseeded Ukrainian.

"I've been working really hard on it," Williams said of her serve. "I'm glad it's coming through. I hope I can keep it up for the rest of the tournament and the US Open." Clijsters, back after a two-year absence from tennis, kept her comeback on course with a 6-2, 7-5 victory over Switzerland's Patty Schnyder.

Clijsters booked a third-round clash with Russia's French Open champion Svetlana Kuznetsova.

Clijsters, who retired in May of 2007 and gave birth to a daughter in February of 2008, had launched her return with a straight sets victory over France's Marion Bartoli on Monday.

The Belgian, who claimed her only Grand Slam title at the 2005 US Open, was never broken by Schnyder, ranked 20th in the world.

"Does it look easy?" Clijsters said. "I started off playing well. It's a really good feeling. I'm moving well. I'm very happy with the way I'm starting. It helps your confidence to get into a rhythm." If the 26-year-old can get past Kuznetsova she faces a possible quarter-final clash against top-seeded Russian Dinara Safina.

Clijsters has won six of her seven career matches against Kuznetsova.

"I knew coming in that this was a big tournament," said Clijsters, who received a wild card. "I knew it was going to be tough from the start, and I'm glad I'm still going. Patty's a good player. We've had a lot of tough matches, a lot of three-setters, so I'm glad I got out in two." Fourth-seeded Russian Elena Dementieva, the Olympic singles gold medallist, advanced with a 6-3, 6-4 victory over Belgian qualifier Yanina Wickmayer.

Fifth-seeded Jelena Jankovic of Serbia opened her campaign with a 7-6 (8/6), 6-3 second-round victory over Russian Maria Kirilenko.

"First match for me, it's never easy," Jankovic said. "It takes time to get used to the conditions - to playing matches again." In other early action, seventh-seeded Russian Vera Zvonareva survived a second-set wobble to get past compatriot Alisa Kleybanova 6-4, 1-6, 7-5.

Ninth-seeded Victoria Azarenka of Belarus downed Russian Anna Chakvetadze 6-4, 6-2. Slovakian Daniela Hantuchova advanced with a 7-5, 1-6, 6-4 victory over Ukraine's Alona Bondarenko, while China's Peng Shuai downed Spain's Maria Jose Martinez Sanchez 5-7, 6-2, 6-1.

Peng set up a third-round clash with Safina, a three-set winner over Italy's Roberta Vinci on Tuesday.

Fourteenth-seeded Italian Flavia Pennetta, who lifted the trophy in Los Angeles last week, defeated Hungary's Agnes Szavay 6-2, 6-4 to advance to a meeting with third-seeded American Venus Williams.

Hungary's Melinda Czink notched the upset of the day, toppling 11th-seeded Serb Ana Ivanovic 7-6 (8/6), 7-5.