Romania's Simona Halep returns the ball to Switzerland's Belinda Bencic during their WTA Madrid Open semi-final tennis match at the Caja Magica in Madrid on May 10, 2019. (Photo by GABRIEL BOUYS / AFP via Getty Images)

Spain's Rafael Nadal celebrates after beating US Frances Tiafoe after their ATP Madrid Open round of 16 tennis match at the Caja Magica in Madrid on May 9, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

TOPSHOT - Spain's Rafael Nadal celebrates after beating US Frances Tiafoe after their ATP Madrid Open round of 16 tennis match at the Caja Magica in Madrid on May 9, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

Serbia's Novak Djokovic celebrates after defeating France's Jeremy Chardy during their ATP Madrid Open round of 16 tennis match at the Caja Magica in Madrid on May 9, 2019. (Photo by GABRIEL BOUYS / AFP via Getty Images)

TOPSHOT - France's Gael Monfils reacts during his ATP Madrid Open round of 16 tennis match against Switzerland's Roger Federer at the Caja Magica in Madrid on May 9, 2019. (Photo by GABRIEL BOUYS / AFP via Getty Images)

TOPSHOT - France's Gael Monfils serves the ball to Switzerland's Roger Federer during their ATP Madrid Open round of 16 tennis match against Switzerland's Roger Federer at the Caja Magica in Madrid on May 9, 2019. (Photo by GABRIEL BOUYS / AFP via Getty Images)

TOPSHOT - Switzerland's Roger Federer returns the ball to France's Gael Monfils during their ATP Madrid Open round of 16 tennis match at the Caja Magica in Madrid on May 9, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)

TOPSHOT - Switzerland's Roger Federer returns the ball to France's Gael Monfils during their ATP Madrid Open round of 16 tennis match at the Caja Magica in Madrid on May 9, 2019. (Photo by OSCAR DEL POZO / AFP via Getty Images)