Stefanos Tsitsipas of Greece returns the ball against Alexander Zverev of Germany during the quarterfinal match of men's singles at the 2018 Rogers Cup in Toronto, Canada, Aug. 10, 2018. Stefanos Tsitsipas of Greece won 2-1. (Xinhua/Zou Zheng)

Kevin Anderson of South Africa celebrates victory after the quarterfinal match of men's singles against Grigor Dimitrov of Bulgaria at the 2018 Rogers Cup in Toronto, Canada, Aug. 10, 2018. Kevin Anderson of South Africa won 2-0. (Xinhua/Zou Zheng)

Kevin Anderson of South Africa returns the ball against Grigor Dimitrov of Bulgaria during the quarterfinal match of men's singles at the 2018 Rogers Cup in Toronto, Canada, Aug. 10, 2018. Kevin Anderson of South Africa won 2-0. (Xinhua/Zou Zheng)

Kevin Anderson of South Africa returns the ball against Grigor Dimitrov of Bulgaria during the quarterfinal match of men's singles at the 2018 Rogers Cup in Toronto, Canada, Aug. 10, 2018. Kevin Anderson of South Africa won 2-0. (Xinhua/Zou Zheng)

Alexander Zverev of Germany returns the ball against Stefanos Tsitsipas of Greece during the quarterfinal match of men's singles at the 2018 Rogers Cup in Toronto, Canada, Aug. 10, 2018. Alexander Zverev of Germany lost 1-2. (Xinhua/Zou Zheng)

Grigor Dimitrov of Bulgaria reacts during the quarterfinal match of men's singles against Kevin Anderson of South Africa at the 2018 Rogers Cup in Toronto, Canada, Aug. 10, 2018. Grigor Dimitrov of Bulgaria lost 0-2. (Xinhua/Zou Zheng)

Grigor Dimitrov of Bulgaria serves against Kevin Anderson of South Africa during the quarterfinal match of men's singles at the 2018 Rogers Cup in Toronto, Canada, Aug. 10, 2018. Grigor Dimitrov of Bulgaria lost 0-2. (Xinhua/Zou Zheng)

Stefanos Tsitsipas of Greece returns the ball against Alexander Zverev of Germany during the quarterfinal match of men's singles at the 2018 Rogers Cup in Toronto, Canada, Aug. 10, 2018. Stefanos Tsitsipas of Greece won 2-1. (Xinhua/Zou Zheng)

Stefanos Tsitsipas of Greece celebrates victory after the quarterfinal match of men's singles against Alexander Zverev of Germany at the 2018 Rogers Cup in Toronto, Canada, Aug. 10, 2018. Stefanos Tsitsipas of Greece won 2-1. (Xinhua/Zou Zheng)

Alexander Zverev of Germany reacts during the quarterfinal match of men's singles against Stefanos Tsitsipas of Greece at the 2018 Rogers Cup in Toronto, Canada, Aug. 10, 2018. Alexander Zverev of Germany lost 1-2. (Xinhua/Zou Zheng)