Novak Djokovic of Serbia loses his racket during the men's singles second round match against Ito Tatsuma of Japan at the 2020 Australian Open tennis tournament in Melbourne, Australia, Jan. 22, 2020.

Novak Djokovic of Serbia celebrates after winning the men's singles second round match against Ito Tatsuma of Japan at the 2020 Australian Open tennis tournament in Melbourne, Australia, Jan. 22, 2020.

Alison Riske of the United States hits a return during the women's singles second round match against Zhu Lin of China at the 2020 Australian Open tennis tournament in Melbourne, Australia, Jan. 22, 2020.

Alison Riske of the United States serves during the women's singles second round match against Zhu Lin of China at the 2020 Australian Open tennis tournament in Melbourne, Australia, Jan. 22, 2020.

Caroline Wozniacki of Denmark reacts during the women's singles second round match against Dayana Yastremska of Ukraine at the 2020 Australian Open tennis tournament in Melbourne, Australia, Jan. 22, 2020.

Caroline Wozniacki of Denmark reacts after winning the women's singles second round match against Dayana Yastremska of Ukraine at the 2020 Australian Open tennis tournament in Melbourne, Australia, Jan. 22, 2020.

Dayana Yastremska of Ukraine gets medical treatment during the women's singles second round match against Caroline Wozniacki of Denmark at the 2020 Australian Open tennis tournament in Melbourne, Australia, Jan. 22, 2020.

Dayana Yastremska of Ukraine reacts during the women's singles second round match against Caroline Wozniacki of Denmark at the 2020 Australian Open tennis tournament in Melbourne, Australia, Jan. 22, 2020.

Ito Tatsuma of Japan returns a shot during the men's singles second round match against Novak Djokovic of Serbia at the 2020 Australian Open tennis tournament in Melbourne, Australia, Jan. 22, 2020. (Photos: Xinhua)

Ito Tatsuma of Japan reacts during the men's singles second round match against Novak Djokovic of Serbia at the 2020 Australian Open tennis tournament in Melbourne, Australia, Jan. 22, 2020.