Kerber dropped a 6-2, 6-1 decision to Vesna Manasieva and Akgul Amanmuradova swept by Obziler, 6-4, 6-2.
Top-seeded Agnieszka Radwanska advanced to Friday's quarterfinals with a 6-2, 6-2 win over Anne Kremer and will go against local favorite Tamarine Tanasugarn, who escaped with a 4-6, 6-4, 6-4 victory over Olga Poutchkova in her second-round match.
In addition to the Radwanska-Tanasugarn match, other quarterfinal pairings Friday have Chan playing Amanmuradova, Craybas going against Klepac and Manasieva meeting Bychkova.
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