MADRID, SPAIN - MAY 09: Kei Nishikori of Japan returns in his match against Stan Wawrinka of Switzerland during day six of the Mutua Madrid Open at La Caja Magica on May 09, 2019 in Madrid, Spain. (Photo by Alex Pantling/Getty Images)
MADRID, SPAIN - MAY 09: Kei Nishikori of Japan returns in his match against Stan Wawrinka of Switzerland during day six of the Mutua Madrid Open at La Caja Magica on May 09, 2019 in Madrid, Spain. (Photo by Alex Pantling/Getty Images)