Defending champion Dominika Cibulkova bounced back from a slow start to progress to the second round of the Kremlin Cup.
Cibulkova dropped the first set against Russia's Ekaterina Makarova but she held her nerve to triumph 2-6 6-4 6-2.
In a late-night epic, Simona Halep shocked sixth-seeded Nadia Petrova 3-6 7-5 7-5 - the match taking three hours and eight minutes and finishing after midnight local time.
Serbian qualifier Vesna Dolonc reached the next round with a 1-6 6-1 6-4 victory over Galina Voskoboeva, while Yaroslava Shvedova, Tsvetana Pironkova and Alize Cornet recorded straight-set wins.
Shvedova defeated Anastasia Pavlyuchenkova 6-2 6-2, Pironkova toppled Varvara Lepchenko 6-0 7-6 (7-3) and Cornet brushed aside Anastasia Rodionova 6-4 6-3.