Wozniacki was very solid in a 6-3, 6-1 victory over fourth-seeded Roberta Vinci. That put Wozniacki at 2-0 in group play with a chance to complete the round-robin unbeaten on Thursday.
She is in control in Group Serdika as Vinci is 1-1 and fifth-seeded Hsieh Su-Wei and Daniela Hantuchova, seeded seventh, are both 0-1.
Petrova, the No. 2 seed, beat sixth-seeded Zheng Jie 6-3, 6-3 and Kirilenko, who is seeded third, beat No. 8-seeded Tsvetana Pironkova 6-1, 6-4. They are 1-0 in Group Sredets with Pironkova 1-1 and Zheng 0-2.
Wozniacki saw only two break points Wednesday as she dropped just 10 points over eight games serving. Three of those came in the second set when Wozniacki quickly closed out Vinci in 68 minutes.
Petrova had seven breaks in Zheng's nine games serving. She won 59 percent of the points when receiving serve.
Kirilenko opened her tournament by getting five breaks against Pironkova. She established control by taking more than 60 percent of the points in the first set.
Wozniacki wraps up her group play Thursday against Hantuchova while Vinci takes on Hsieh. The first match of the day sends Petrova against Kirilenko.