Vaidisova, seeded third, lost the first in the tiebreaker before putting away Ekaterina Makarova 6-7 (5-7), 6-2, 6-4. Bondarenko, seeded fifth, stumbled to a 3-6 first-set loss and then rallied for the 3-65, 7-5, 6-1 win over Sunitha Rao.
Two seeded players were ousted with No. 8 Michaella Krajicek falling 6-3, 6-4 to Yanina Wickmayer and 17th-seeded Aiko Nakamura losing 2-6, 6-4, 6-4 to Melanie South.
Friday's quarterfinals will pit Vaidisova against Mattek, Alona Bondarenko versus Erakovic, Kateryna Bondarenko against Cetkovska and Wickmayer versus South.
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