Alexander Zverev of Germany hits a return during the men's singles quarterfinal match between Alexander Zverev of Germany and Alex De Minaur of Australia at the 2019 ATP Mexican Open tennis tournament in Acapulco, Mexico, on Feb. 28, 2019. Alexander Zverev won 2-0. (Xinhua/Xin Yuewei)

Alexander Zverev of Germany serves during the men's singles quarterfinal match between Alexander Zverev of Germany and Alex De Minaur of Australia at the 2019 ATP Mexican Open tennis tournament in Acapulco, Mexico, on Feb. 28, 2019. Alexander Zverev won 2-0. (Xinhua/Xin Yuewei)

Alex De Minaur of Australia serves during the men's singles quarterfinal match between Alexander Zverev of Germany and Alex De Minaur of Australia at the 2019 ATP Mexican Open tennis tournament in Acapulco, Mexico, on Feb. 28, 2019. Alexander Zverev won 2-0. (Xinhua/Xin Yuewei)

Alex De Minaur of Australia hits a return during the men's singles quarterfinal match between Alexander Zverev of Germany and Alex De Minaur of Australia at the 2019 ATP Mexican Open tennis tournament in Acapulco, Mexico, on Feb. 28, 2019. Alexander Zverev won 2-0. (Xinhua/Xin Yuewei)

Alexander Zverev of Germany hits a return during the men's singles quarterfinal match between Alexander Zverev of Germany and Alex De Minaur of Australia at the 2019 ATP Mexican Open tennis tournament in Acapulco, Mexico, on Feb. 28, 2019. Alexander Zverev won 2-0. (Xinhua/Xin Yuewei)

Alexander Zverev of Germany reacts during the men's singles quarterfinal match between Alexander Zverev of Germany and Alex De Minaur of Australia at the 2019 ATP Mexican Open tennis tournament in Acapulco, Mexico, on Feb. 28, 2019. Alexander Zverev won 2-0. (Xinhua/Xin Yuewei)

Alexander Zverev of Germany hits a return during the men's singles quarterfinal match between Alexander Zverev of Germany and Alex De Minaur of Australia at the 2019 ATP Mexican Open tennis tournament in Acapulco, Mexico, on Feb. 28, 2019. Alexander Zverev won 2-0. (Xinhua/Xin Yuewei)