CINCINNATI, OH, USA - The first round rounded up and the second round began at the Western & Southern Financial Group Women's Open on Tuesday, with the night matches featuring a star-studded line-up.

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Leading the first round winners were Top 20 players Flavia Pennetta and Yanina Wickmayer, both moving through in straight sets. Pennetta, the No.11 seed, beat former Top 20 player Zheng Jie, 64 62, while Wickmayer, the No.12 seed, rolled past qualifier Greta Arn in an early match, 62 62.

"It was hot and humid out there but I handled it well," said Wickmayer, who reached the second round at this stop for the third straight year. "Today I played one of my best matches of the year. I'm really happy with my form."

See the best off-court pics from Cincinnati here in the gallery!

The only other seed in first round action wasn't so fortunate, as No.15 seed Nadia Petrova had to retire in the second set against young American wildcard Christina McHale due to heat illness. Petrova was down a set and 5-3.

"I'm just excited to move onto the next round," McHale, just 18 years old from New Jersey, said. "I was just trying to stay cool in the heat. I drank a lot, put some ice packs on my neck, changed my outfit after the first set... I think I handled it well. I remember the heat in Australia being like this last year."

Other daytime first round winners were Anastasia Pavlyuchenkova, Maria Kirilenko, Andrea Petkovic, Gisela Dulko, Elena Vesnina and Sybille Bammer. Vesnina cruised against American Melanie Oudin, 62 63.

"I played in Istanbul the week before this and it was also very hot,," Vesnina said. "I think today was maybe one of the hottest days of my life!"

Oudin commented on the pressure of being the breakthrough star of last year's US Open, where she reached her first Grand Slam quarterfinal: "I'm hoping the hype won't be that bad this year, but I have a feeling it's going to be. People are going to expect I can do it again. But this year I'm going to go into it just like last year - that's how I did so well. No expectations. Last year I saw my draw before the tournament and my coach looked at me and said, 'To win, you have to beat six Russians and a Williams sister.' It was a joke. To beat them last year was amazing, but I had no pressure on me and I just went for it."

See pics of Oudin hitting on Cincinnati's tallest skyscraper here!

The first round wrapped up at night with No.10 seed Maria Sharapova winning a streaky match against Svetlana Kuznetsova, 64 16 62. Kuznetsova was coming off her first title of the year in San Diego; she played a strong second set but after falling behind 3-0 in the decider couldn't catch up.

"It's definitely tough to have a night flight then come and play the day after a final, but it's just bad luck, I cannot change it," Kuznetsova said afterwards. "I just need to get my ranking higher and then I can get a bye. But I also have to give a lot of credit to Maria. She played really well in the third."

"I let her off the hook in the beginning of the second set, and she went with it. Against a player with a lot of experience, you can't do that," Sharapova said. "I had to earn it. The only way I was going to win was by being aggressive."