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)

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 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)

TOPSHOT - 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 OSCAR DEL POZO / AFP via Getty Images)

TOPSHOT - 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)