TOPSHOT - This multiexposure picture shows Romania's Simona Halep returning the ball to Australia's Ashleigh Barty during their WTA Madrid Open round of 8 tennis match at the Caja Magica in Madrid on May 9, 2019. Two-time champion Simona Halep overcame Ashleigh Barty 7-5, 7-5 to reach her fourth Madrid Open semi-final today. Romania's third seed and former number one will next play the winner from top seed Naomi Osaka and on-form Swiss Belinda Bencic. (Photo by GABRIEL BOUYS / AFP via Getty Images)

TOPSHOT - Spain's Rafael Nadal attends a training session during the ATP Madrid Open at the Caja Magica in Madrid on May 7, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Serbia's Novak Djokovic (R) and Greece's Stefanos Tsitsipas (L) pose on the podium of the 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 (R) and Greece's Stefanos Tsitsipas (L) pose 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 holds 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 (L) shakes hands with es 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 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 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)