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HALLE, GERMANY - JUNE 21: Alexander Zerev of Germany plays a back hand during his match against Philipp Kohlschreiber of Germany during Day 5 of the Gerry Weber Open 2017 at Gerry Weber Stadium on June 21, 2017 in Halle, Germany. (Photo by Lars Baron/Bongarts/Getty Images)

HALLE, GERMANY - JUNE 21:  Alexander Zerev of Germany plays a back hand during his match against Philipp Kohlschreiber of Germany during Day 5 of the Gerry Weber Open 2017 at Gerry Weber Stadium on June 21, 2017 in Halle, Germany.  (Photo by Lars Baron/Bongarts/Getty Images)