MELBOURNE, Australia - They had injury scares in the lead-up tournaments but Kim Clijsters and Caroline Wozniacki both had few problems in their first round matches at the big one on Monday, easing into the second round.

Clijsters, the No.11 seed, was the first to advance, edging Portuguese qualifier Maria Joao Koehler in a 42-minute first set then rolling to a 75 61 win. The lefty Koehler held onto her first five service games before Clijsters broke the match open, winning eight of the last nine games for a straight set triumph.

"It was hard to read her serve and get used to a player I'd never played before. I really had to find my rhythm out there," Clijsters said after the match. "But I was excited to go out there and start playing again. I've had that since we came to Australia. I had a good off-season and wanted to put it to the test.

In her only lead-up event, Clijsters reached the semifinals of Brisbane before retiring against Daniela Hantuchova due to a left hip injury. The injury turned out to be a sprained muscle, but the Belgian says it's not a problem now. "I'm happy it's over with. It's something we'll keep a close eye on, and I still get treated every day, so we make sure all the muscles around it are strong, the ones that need to be loosened up are loosened up, try to keep that balance."

In the late night match, No.1 seed Wozniacki pulled away from 2-all in the first set and fought off some pinpoint crosscourt forehands to get past Russian-born Australian Anastasia Rodionova, 62 60. Wozniacki had struggled with a wrist injury during a quarterfinal loss at the lead-up event in Sydney.

"I was a bit nervous before the match. I didn't know exactly what to expect. But it feels better," Wozniacki said of her wrist. "I'm very happy about the way I felt out there today. I got into the rhythm as the match went on tonight."

Another big name joining Clijsters and Wozniacki in a loaded top quarter is Li Na. The No.5-seeded Chinese, who reached her first WTA final since winning the French Open in Sydney last week, beat Ksenia Pervak, 63 61.

"I was trusting myself, believing in myself to win the match," Li commented. "But this week is another story. It has nothing to do with how I was doing in Perth or Sydney. This tournament is even bigger, even more important. For me it's just one thing at a time. Round by round, step by step."

No.10 seed Francesca Schiavone, No.13 seed Jelena Jankovic and No.16 seed Peng Shuai were also among the winners later in the day.

The first day of play also brought the first wave of upsets, with Russian qualifier Nina Bratchikova upsetting No.19 seed Flavia Pennetta, 63 16 62, her first Top 20 win; American teenager Christina McHale surprising No.24 seed and former Australian Open quarterfinalist Lucie Safarova, 62 64; and Galina Voskoboeva taking out No.28 seed Yanina Wickmayer, 75 62.

No.3 seed Victoria Azarenka and No.8 seed Agnieszka Radwanska won through earlier in the day. Read more about their wins here.