Bethanie Mattek-Sands of the U.S. plays a forehand shot in her match against compatriot Madison Keys during the Sydney International tennis tournament in Sydney, Australia, Wednesday, Jan. 8, 2014. Officials say Mattek-Sands retired from the match with a lower back injury. (AP Photo/Rob Griffith)

Australia Tennis Sydney International

Bethanie Mattek-Sands of the U.S. plays a forehand shot in her match against compatriot Madison Keys during the Sydney International tennis tournament in Sydney, Australia, Wednesday, Jan. 8, 2014. Officials say Mattek-Sands retired from the match with a lower back injury. (AP Photo/Rob Griffith)

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