Ivanovic, looking for her third ToC title in the last four years, improved to 2-0 in Group B play with a 6-2, 5-7, 6-2 victory over fourth-seeded Samantha Stosur. Ivanovic had a pair of breaks in the first set and three more in the third in the win.
While she leads the group, Ivanovic is yet to lock up a spot in the semifinals. A win Friday over fifth-seeded Elena Vesnina would do that, however.
Vesnina and Stosur are tied at 1-1 in the group. Tsvetana Pironkova, seeded eighth, is 0-2 going into her final round-robin match against Stosur.
Vesnina defeated Pironkova 6-2, 4-6, 6-0 Thursday. Vesnina took just less than half -- 44-of-90 -- of the points when Pironkova served.
Thursday's play wrapped with top-seeded Simona Halep completing a Group A sweep by beating Elina Svitolina 6-1, 6-1 in 47 minutes. Halep won nearly three-quarters of the points and had seven breaks off Svitolina's serve.