Switzerland's Roger Federer celebrates after defeating 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 GABRIEL BOUYS / AFP via Getty Images)

Switzerland's Belinda Bencic serves the ball to Japan's Naomi Osaka during their WTA Madrid Open round of 8 tennis match at the Caja Magica in Madrid on May 9, 2019. (Photo by GABRIEL BOUYS / AFP via Getty Images)

Japan's Naomi Osaka returns the ball to Switzerland's Belinda Bencic during their WTA Madrid Open round of 8 tennis match at the Caja Magica in Madrid on May 9, 2019. (Photo by GABRIEL BOUYS / AFP via Getty Images)

Japan's Naomi Osaka serves the ball to Switzerland's Belinda Bencic during their WTA Madrid Open round of 8 tennis match at the Caja Magica in Madrid on May 9, 2019. (Photo by GABRIEL BOUYS / AFP via Getty Images)

Japan's Naomi Osaka serves the ball to Switzerland's Belinda Bencic during their WTA Madrid Open round of 8 tennis match at the Caja Magica in Madrid on May 9, 2019. (Photo by GABRIEL BOUYS / AFP via Getty Images)

Japan's Naomi Osaka returns the ball to Switzerland's Belinda Bencic during their WTA Madrid Open round of 8 tennis match at the Caja Magica in Madrid on May 9, 2019. (Photo by GABRIEL BOUYS / AFP via Getty Images)

Romania's Simona Halep serves 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)

Romania's Simona Halep returns 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)