MASON, OH - AUGUST 15: Stan Wawrinka of Switzerland returns a shot to Kei Nishikori of Japan during Day 5 of the Western and Southern Open at the Lindner Family Tennis Center on August 15, 2018 in Mason, Ohio. (Photo by Rob Carr/Getty Images)
MASON, OH - AUGUST 15: Stan Wawrinka of Switzerland returns a shot to Kei Nishikori of Japan during Day 5 of the Western and Southern Open at the Lindner Family Tennis Center on August 15, 2018 in Mason, Ohio. (Photo by Rob Carr/Getty Images)