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GUANGZHOU, CHINA - MARCH 20: Ze Zhang of China serves during the match against Lukas Lacko of Slovakia during the 2016 'GDD CUP' International ATP Challenger Guangzhou Tour Day 6 at Guangzhou Development District International Tennis School on March 20, 2016 in Guangzhou, China. (Photo by Zhong Zhi/Getty Images)

GUANGZHOU, CHINA - MARCH 20: Ze Zhang of China serves during the match against Lukas Lacko of Slovakia during the 2016 'GDD CUP' International ATP Challenger Guangzhou Tour Day 6 at Guangzhou Development District International Tennis School on March 20, 2016 in Guangzhou, China. (Photo by Zhong Zhi/Getty Images)