Second seed Garbine Muguruza joined defending champion Maria Sharapova and world number two Simona Halep on the Brisbane International sidelines after retiring hurt in her match against Varvara Lepchenko Wednesday.
Lepchenko won a thrilling first set 7-6 (11/9) and was leading 1-0 in the second when Muguruza pulled out with blisters on her feet.
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Muguruza had called for the trainer after the first set to have her left foot bandaged but her movement was hampered in the first game of the second set and she decided she couldn't continue.
Sharapova and Halep both withdrew from the tournament before their opening matches, Sharapova with an arm injury and Halep with a sore Achilles.
Their withdrawals mean fourth seed Angelique Kerber is the highest ranked player left in the tournament.
Lepchenko will face another Spaniard, Carla Suarez Navarro, in the quarter-finals.