Russia's Aslan Karatsev competes during the men's singles semifinal between Serbia's Novak Djokovic and Russia's Aslan Karatsev at Australian Open in Melbourne Park in Melbourne, Australia, Feb. 18, 2021. (Xinhua/Bai Xuefei)

Jennifer Brady of the United States competes during the women's singles semifinal between Karolina Muchova of the Czech Republic and Jennifer Brady of the United States at Australian Open in Melbourne Park in Melbourne, Australia, Feb. 18, 2021. (Photo by Hu Jingchen/Xinhua)

Serbia's Novak Djokovic competes during the men's singles semifinal between Serbia's Novak Djokovic and Russia's Aslan Karatsev at Australian Open in Melbourne Park in Melbourne, Australia, Feb. 18, 2021. (Xinhua/Bai Xuefei)

Russia's Aslan Karatsev competes during the men's singles semifinal between Serbia's Novak Djokovic and Russia's Aslan Karatsev at Australian Open in Melbourne Park in Melbourne, Australia, Feb. 18, 2021. (Xinhua/Bai Xuefei)

Jennifer Brady of the United States celebrates after the women's singles semifinal between Karolina Muchova of the Czech Republic and Jennifer Brady of the United States at Australian Open in Melbourne Park in Melbourne, Australia, Feb. 18, 2021. (Photo by Hu Jingchen/Xinhua)

Russia's Aslan Karatsev competes during the men's singles semifinal between Serbia's Novak Djokovic and Russia's Aslan Karatsev at Australian Open in Melbourne Park in Melbourne, Australia, Feb. 18, 2021. (Xinhua/Bai Xuefei)

Russia's Aslan Karatsev competes during the men's singles semifinal between Serbia's Novak Djokovic and Russia's Aslan Karatsev at Australian Open in Melbourne Park in Melbourne, Australia, Feb. 18, 2021. (Xinhua/Bai Xuefei)

Serbia's Novak Djokovic serves during the men's singles semifinal between Serbia's Novak Djokovic and Russia's Aslan Karatsev at Australian Open in Melbourne Park in Melbourne, Australia, Feb. 18, 2021. (Xinhua/Bai Xuefei)

Jennifer Brady of the United States celebrates after the women's singles semifinal between Karolina Muchova of the Czech Republic and Jennifer Brady of the United States at Australian Open in Melbourne Park in Melbourne, Australia, Feb. 18, 2021. (Photo by Hu Jingchen/Xinhua)