Stosur wins to reach semis in Sofia

Sofia, Bulgaria ( - Former U.S. Open champion Samantha Stosur was among those on Friday securing a semifinal berth at the season- ending WTA Tournament of Champions.

In the final round-robin match of the week in Sofia, the fourth-seeded Stosur (2-1) captured her group by handling eighth-seeded Bulgarian crowd favorite Tsvetana Pironkova 6-1, 6-4 to move into the semifinals. Pironkova went 0-3 this week.

Meanwhile, a Day 4 upset came when fifth-seeded Russian Elena Vesnina (2-1) topped second-seeded former world No. 1 Ana Ivanovic 6-4, 3-6, 7-6 (7-1). Despite the result, the two-time Tournament of Champions titlist Ivanovic (2-1) qualified for the semis, while Vesnina's week, and season, came to an end on Friday.

The former French Open titlist Ivanovic captured this Tournament of Champions event back-to-back in 2010 and 2011 in Bali.

Also on Friday, sixth-seeded Russian Anastasia Pavlyuchenkova (2-1) booked a spot in the semis by leveling seventh-seeded Frenchwoman Alize Cornet 6-2, 6-2.

Saturday's semifinals will pit top-seeded Romanian star Simona Halep against the Serbian Ivanovic and the Aussie Stosur versus Pavlyuchenkova.

This tournament features an eight-woman field that was divided into two groups. Round-robin play was staged through Friday.

"Group Serdika" featured Halep (3-0), third-seeded Russian Maria Kirilenko (0-1), Pavlyuchenkova and Cornet (1-2). An injured Kirilenko was replaced in the field earlier in the week by winless Ukrainian Elina Svitolina (0-2).

"Group Sredets" was comprised of Ivanovic, Stosur, Vesnina, and Pironkova.

The field consisted 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 weekend's Fed Cup final. Ivanovic and Pironkova came on board as wild cards.