John Millman of Australia returns the ball during the men's singles first round match with Alexander Zverev of Germany at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. John Millman lost 2-3. (Xinhua/Han Yan)

John Millman of Australia returns the ball during the men's singles first round match with Alexander Zverev of Germany at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. John Millman lost 2-3. (Xinhua/Han Yan)

John Millman of Australia returns the ball during the men's singles first round match with Alexander Zverev of Germany at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. John Millman lost 2-3. (Xinhua/Han Yan)

John Millman of Australia reacts during the men's singles first round match with Alexander Zverev of Germany at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. John Millman lost 2-3. (Xinhua/Han Yan)

John Millman of Australia reacts during the men's singles first round match with Alexander Zverev of Germany at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. John Millman lost 2-3. (Xinhua/Han Yan)

John Millman of Australia returns the ball during the men's singles first round match with Alexander Zverev of Germany at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. John Millman lost 2-3. (Xinhua/Han Yan)

John Millman of Australia reacts during the men's singles first round match with Alexander Zverev of Germany at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. John Millman lost 2-3. (Xinhua/Han Yan)

Alexander Zverev of Germany returns the ball during the men's singles first round match with John Millman of Australia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. Alexander Zverev won 3-2. (Xinhua/Han Yan)

Alexander Zverev of Germany returns the ball during the men's singles first round match with John Millman of Australia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. Alexander Zverev won 3-2. (Xinhua/Han Yan)

Alexander Zverev of Germany returns the ball during the men's singles first round match with John Millman of Australia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. Alexander Zverev won 3-2. (Xinhua/Han Yan)

Alexander Zverev of Germany returns the ball during the men's singles first round match with John Millman of Australia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. Alexander Zverev won 3-2. (Xinhua/Han Yan)

Alexander Zverev of Germany returns the ball during the men's singles first round match with John Millman of Australia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. Alexander Zverev won 3-2. (Xinhua/Han Yan)

Alexander Zverev of Germany celebrates after winning the men's singles first round match with John Millman of Australia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. Alexander Zverev won 3-2. (Xinhua/Han Yan)

Alexander Zverev of Germany reacts during the men's singles first round match with John Millman of Australia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. Alexander Zverev won 3-2. (Xinhua/Han Yan)

Alexander Zverev of Germany reacts during the men's singles first round match with John Millman of Australia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. Alexander Zverev won 3-2. (Xinhua/Han Yan)

Alexander Zverev of Germany returns the ball during the men's singles first round match with John Millman of Australia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 28, 2019. Alexander Zverev won 3-2. (Xinhua/Han Yan)