MADRID, SPAIN - MAY 03: Juan Martin Del Potro of Argentina serves to Dominic Thiem of Austria during day four of the Mutua Madrid Open tennis tournament at the Caja Magica on May 03, 2016 in Madrid, Spain. (Photo by Julian Finney/Getty Images)
MADRID, SPAIN - MAY 03: Juan Martin Del Potro of Argentina serves to Dominic Thiem of Austria during day four of the Mutua Madrid Open tennis tournament at the Caja Magica on May 03, 2016 in Madrid, Spain. (Photo by Julian Finney/Getty Images)