SOFIA, Bulgaria (AP) Garbine Muguruza moved a step closer to the semifinals by beating favorite Flavia Pennetta of Italy 0-6, 6-1, 6-1 in the group stage at the season-ending WTA Tournament of Champions on Thursday.
The seventh-seeded Spanish player, who broke serve five times and saved 10 of 13 break points on her own serve, is now the only undefeated player in her Serdika group.
Muguruza will wrap up her round robin schedule on Friday against Alize Cornet of France who stayed alive in her bid for a semifinal spot by defeating top-seeded Ekaterina Makarova of Russia 6-1, 6-4.
Makarova announced after the match that she was withdrawing from the tournament because of an injury.
''Unfortunately I have to withdraw with a back injury which happened in Singapore,'' she said. ''I tried my best tennis, but it is not possible for me to play at my highest level right now.''
The No. 11 in the WTA ranking lost her opening game on Wednesday in staright sets to Garbine Muguruza. She will be replaced by Karolina Pliskova of the Czech Republic, who plays Flavia Pennetta on Friday.
Dominika Cibulkova of Slovakia is facing Germany's Andrea Petkovic later on Thursday in the Sredets group.