Vera Zvonareva cruised into the quarterfinals of the Baku Cup on Thursday when Kristina Kucova retired with a left leg injury.
The top-seeded Russian was leading 6-0, 3-0 when Kucova quit. Although she was playing with the lower part of her left leg heavily strapped the Slovak had shown no sign of struggling with her fitness.
She ran well in the rallies but made little headway against a more powerful and skillful opponent, managing to salvage just 10 points in the first set and challenging Zvonareva only briefly by holding a break point when down 2-0 in the second set.
Anastasia Pavlyuchenkova survived early pressure from fellow Russian Elena Bovina, winning 6-4, 6-0.
The second-seeded Pavlyuchenkova struggled at the start as Bovina broke to lead 2-0 and then held a break point for a 4-0 lead. But Pavlyuchenkova fought back and began to gain the upper hand with her more aggressive game forcing an increasing number of errors from her opponent.
After securing the opening set, Pavlyuchenkova lost just nine points as she breezed through the second.
Kateryna Bondarenko continued her recent good form by upsetting fourth-seeded Ekaterina Makarova of Russia 6-1, 6-4.
The Ukrainian endured a miserable first half of the year, winning two matches in her opening tournament of the season in Auckland but then failing to win another main draw match until Wimbledon last month.
She was by far the stronger player against Makarova, who was listless and made a succession of clumsy errors.
Georgia's Anna Tatishvili also advanced to the quarterfinals when she defeated compatriot Tatia Mikadze 7-6 (4), 6-3.
In Friday's quarterfinals Zvonareva plays Tatishvili, Pavlyuchenkova faces Kahzak Galina Voskoboeva, Bondarenko tackles Mariya Korryttseva in an all-Ukrainian clash, and Russia's Ksenia Pervak meets Aravane Rezai of France.