Austria's Dominic Thiem serves to Serbia's Novak Djokovic during their ATP Madrid Open semi-final tennis match at the Caja Magica in Madrid on May 11, 2019. (Photo by JAVIER SORIANO / AFP via Getty Images)

TOPSHOT - Serbia's Novak Djokovic holds with his trophy after winning the ATP Madrid Open final tennis match at the Caja Magica in Madrid on May 12, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

TOPSHOT - Serbia's Novak Djokovic holds his trophy as he poses with children after winning the ATP Madrid Open final tennis match at the Caja Magica in Madrid on May 12, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Serbia's Novak Djokovic (R) conforts Greece's Stefanos Tsitsipas (L) on the podium of the ATP Madrid Open final tennis match at the Caja Magica in Madrid on May 12, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Serbia's Novak Djokovic kisses his trophy after winning the ATP Madrid Open final tennis match against Greece's Stefanos Tsitsipas at the Caja Magica in Madrid on May 12, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Serbia's Novak Djokovic kisses his trophy after winning the ATP Madrid Open final tennis match against Greece's Stefanos Tsitsipas at the Caja Magica in Madrid on May 12, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Serbia's Novak Djokovic celebrates after defeating Greece's Stefanos Tsitsipas after their ATP Madrid Open final tennis match at the Caja Magica in Madrid on May 12, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Serbia's Novak Djokovic celebrates after defeating Greece's Stefanos Tsitsipas during their ATP Madrid Open final tennis match at the Caja Magica in Madrid on May 12, 2019. (Photo by JAVIER SORIANO / AFP via Getty Images)