WASHINGTON, DC - AUGUST 07: Alexander Zverev of Germany reacts during a match against Marin Cilic of Croatia during the Citi Open at Rock Creek Park Tennis Center on August 7, 2015 in Washington, DC. (Photo by Patrick Smith/Getty Images)
WASHINGTON, DC - AUGUST 07: Alexander Zverev of Germany reacts during a match against Marin Cilic of Croatia during the Citi Open at Rock Creek Park Tennis Center on August 7, 2015 in Washington, DC. (Photo by Patrick Smith/Getty Images)