Andrea Petkovic into Sofia semis, Ekaterina Makarova pulls out

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, 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.