Spain's Rafael Nadal gestures in front of Greece's Stefanos Tsitsipas during their ATP Madrid Open semi-final tennis match at the Caja Magica in Madrid on May 11, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Spain's Rafael Nadal returns the ball to Greece's Stefanos Tsitsipas during their ATP Madrid Open semi-final tennis match at the Caja Magica in Madrid on May 11, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Spain's Rafael Nadal runs for the ball against Greece's Stefanos Tsitsipas during their ATP Madrid Open semi-final tennis match at the Caja Magica in Madrid on May 11, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Spain's Rafael Nadal runs for the ball against Greece's Stefanos Tsitsipas during their ATP Madrid Open semi-final tennis match at the Caja Magica in Madrid on May 11, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Netherlands' Kiki Bertens returns the ball to Romania's Simona Halep during their WTA Madrid Open final tennis match at the Caja Magica in Madrid on May 11, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Romania's Simona Halep serves to Netherlands' Kiki Bertens during their WTA Madrid Open final tennis match at the Caja Magica in Madrid on May 11, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Romania's Simona Halep returns the ball to Netherlands' Kiki Bertens during their WTA Madrid Open final tennis match at the Caja Magica in Madrid on May 11, 2019. (Photo by JAVIER SORIANO / AFP via Getty Images)

Serbia's Novak Djokovic celebrates after defeating Austria's Dominic Thiem 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)