Ana Ivanovic made it two wins from two in the round-robin stage of the WTA Tournament of Champions with a 6-2 5-7 6-2 result against Sam Stosur.
The Serbian put herself firmly on course to reach the semi-finals in Sofia, gaining revenge in the process for a loss suffered at the hands of the same opponent in Moscow earlier in October.
Ivanovic, the second seed for the tournament, still has work to do to reach the knockout stages, while Stosur's hopes are not over yet either.
"I played a little bit of a loose game at the end of the second set and was rushing a little bit too much, but I managed to calm down and start fresh in the third set," Ivanovic told the WTA Tour website.
"I started the third set in the same manner as I started the match, so I was very happy about that."
Russia's Elena Vesnina is also still in the hunt to make the last four after she recorded a 6-2 4-6 6-0 win over home hope Tsvetana Pironkova.
With two defeats, Pironkova is out of contention ahead of her third match against Stosur on Friday.
In the other group, Romanian top seed Simona Halep continued her perfect record with a thumping 6-1 6-1 victory over Elina Svitolina.
Halep was already assured of her spot in the last four, while the winner of Friday's clash between Anastasia Pavlyuchenkova and Alize Cornet will finish as runner-up.