Bethanie Mattek-Sands right, of the U.S. shakes hands with compatriot Madison Keys after retiring from their match during the Sydney International tennis tournament in Sydney, Australia, Wednesday, Jan. 8, 2014. Officials said Mattek-Sands retired from the match with a lower back injury. (AP Photo/Rob Griffith)

Australia Tennis Sydney International

Bethanie Mattek-Sands right, of the U.S. shakes hands with compatriot Madison Keys after retiring from their match during the Sydney International tennis tournament in Sydney, Australia, Wednesday, Jan. 8, 2014. Officials said Mattek-Sands retired from the match with a lower back injury. (AP Photo/Rob Griffith)

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