Updated

Sofia, Bulgaria (SportsNetwork.com) - Top seed Simona Halep and former U.S. Open champion Sam Stosur were a pair of straight-set round-robin winners Wednesday at the season-ending WTA Tournament of Champions.

The rising Romanian star Halep handled seventh-seeded Frenchwoman Alize Cornet 6-4, 6-4, while the fourth-seeded Stosur drubbed fifth-seeded Russian Elena Vesnina 6-3, 6-3 on the indoor hardcourt at Armeets Arena.

This event, in its fifth year, features an eight-woman field that is divided into two groups. Round-robin play is staged Tuesday through Friday, with the semifinals on Saturday and a Sunday final.

Group Serdika features Halep (2-0), third-seeded Russian Maria Kirilenko (0-1), sixth-seeded Russian Anastasia Pavlyuchenkova (1-1) and seventh-seeded Frenchwoman Alize Cornet (1-1). An injured Kirilenko was replaced in the field by alternate Elina Svitolina (0-1). Pavlyuchenkova handled the Ukrainian Svitolina 6-2, 6-4 on Wednesday.

Group Sredets is comprised of second-seeded and two-time Tournament of Champions winner Ana Ivanovic (1-0), Stosur (1-0), Vesnina (0-1) and eighth- seeded Tsvetana Pironkova (0-1).

On Thursday, Halep will face Svitolina, the former world No. 1 Ivanovic will encounter Stosur, and Vesnina will battle Pironkova.

The field consists of the six highest-ranked players who won at least one International Series tournament during the year and did not qualify for last week's WTA Championships in Istanbul or are not participating in this week's Fed Cup final. Ivanovic and Pironkova were included this week as wild cards.