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CHENGDU, CHINA - SEPTEMBER 29: Dominic Thiem of Austria serves during the match against Di Wu of China during Day 4 of 2016 ATP Chengdu Open at Sichuan International Tennis Centre on September 29, 2016 in Chengdu, China. (Photo by Zhong Zhi/Getty Images)

CHENGDU, CHINA - SEPTEMBER 29: Dominic Thiem of Austria serves during the match against Di Wu of China during Day 4 of 2016 ATP Chengdu Open at Sichuan International Tennis Centre on September 29, 2016 in Chengdu, China.  (Photo by Zhong Zhi/Getty Images)