Karolina Muchova of the Czech Republic serves to compatriot Karolina Pliskova during their third round match at the Australian Open tennis championship in Melbourne, Australia, Saturday, Feb. 13, 2021.(AP Photo/Andy Brownbill)

United States' Jessica Pegula serves to France's Kristina Mladenovic during their match at the Australian Open tennis championships in Melbourne, Australia, Saturday, Feb. 13, 2021. The Australian Open continues but without crowds after the Victoria state government imposed a five-day lockdown starting Saturday in response to a COVID-19 outbreak at a quarantine hotel. (AP Photo/Hamish Blair)

Fans cheer for Australia's Nick Kyrgios, back to camera, during his third round match against Austria's Dominic Thiem at the Australian Open tennis championship in Melbourne, Australia, Friday, Feb. 12, 2021.(AP Photo/Hamish Blair)

United States' Mackenzie McDonald serves to South Africa's Lloyd Harris during their third round match at the Australian Open tennis championship in Melbourne, Australia, Saturday, Feb. 13, 2021.(AP Photo/Andy Brownbill)

Ukraine's Elina Svitolina celebrates a point against Kazakhstan's Yulia Putintseva during their third round match at the Australian Open tennis championships in Melbourne, Australia, Saturday, Feb. 13, 2021. (AP Photo/Hamish Blair)

A fans holds a placard in support of Australia's Nick Kyrgios during his third round match against Austria's Dominic Thiem at the Australian Open tennis championship in Melbourne, Australia, Friday, Feb. 12, 2021.(AP Photo/Hamish Blair)

Kazakhstan's Yulia Putintseva, left, serves to Ukraine's Elina Svitolina during their third round match at the Australian Open tennis championships in Melbourne, Australia, Saturday, Feb. 13, 2021. The Australian Open continues but without crowds after the Victoria state government imposed a five-day lockdown starting Saturday in response to a COVID-19 outbreak at a quarantine hotel. (AP Photo/Hamish Blair)