Sofia - German fourth seed Andrea Petkovic defeated second-seeded Slovakian Dominika Cibulkova 7-5, 6-3 on Thursday to become the first player to qualify for the semi-finals of the WTA Tournament Of Champions.
Petkovic trailed 3-1 in both sets but hit back on both occasions, closing out the round-robin match in one and 43 minutes.
"I thought I was playing really, really well today (Thursday), and I thought Domi was playing really well too, especially in the first set," Petkovic said. "I'm very happy with my performance out there."
Spanish seventh seed Garbine Muguruza and Alize Cornet, the French sixth seed, won their latest round-robin matches.
Muguruza enjoyed a 0-6, 6-1, 6-1 win over Italian third seed Flavia Pennetta while Cornet saw off top-seeded Ekaterina Makarova of Russia, 6-1, 6-4.
Makarova was later forced to pull out of the tournament because of a back injury.