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HALLE, GERMANY - JUNE 24: Roger Federer of Switzerland plays a backhand during his semi final match against Karen Khachanov of Russia during Day 8 of the Gerry Weber Open 2017 at on June 24, 2017 in Halle, Germany. (Photo by Lars Baron/Bongarts/Getty Images)

HALLE, GERMANY - JUNE 24:  Roger Federer of Switzerland plays a backhand during his semi final match against Karen Khachanov of Russia during Day 8 of the Gerry Weber Open 2017 at  on June 24, 2017 in Halle, Germany.  (Photo by Lars Baron/Bongarts/Getty Images)