Sofia, Bulgaria, 1 November 2013 | AP

Ana Ivanovic overcame Australian Sam Stosur in three sets on Thursday for her second straight victory in the group stage at the season-ending WTA Tournament of Champions in Bulgaria.

The two-time tournament winner and former world No.1 played aggressively to win the opening set 6-2 in just 30 minutes.

Stosur broke Ivanovic’s serve in the second set to go up 5-3. But Ivanovic grabbed the early break at 2-0 in the third set and cruised from there to win 6-2 5-7 6-2.

She will play Russia’s Elena Vesnina on Friday with both players still trying to secure a spot in the semifinals.

Vesnina outlasted Bulgaria’s Tsvetana Pironkova 6-2 4-6 6-0 for her first victory at the tournament.

Stosur next faces Pironkova; a win will secure the Aussie’s spot in the semifinals, regardless of whether it comes in two or three sets.

In Thursday’s last match, top-seeded Simona Halep of Romania swept past Ukraine’s Elina Svitolina 6-1 6-1, to finish the round-robin phase unbeaten. She had already qualified for Saturday’s semis.