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SYDNEY, AUSTRALIA - JANUARY 10: Angelique Kerber of Germany plays a backhand shot in her second round match against Daria Kasatkina of Russia during day three of the 2017 Sydney International at Sydney Olympic Park Tennis Centre on January 10, 2017 in Sydney, Australia. (Photo by Brett Hemmings/Getty Images)

SYDNEY, AUSTRALIA - JANUARY 10:  Angelique Kerber of Germany plays a backhand shot in her second round match against Daria Kasatkina of Russia during day three of the 2017 Sydney International at Sydney Olympic Park Tennis Centre on January 10, 2017 in Sydney, Australia.  (Photo by Brett Hemmings/Getty Images)