Novak Djokovic played through the pain barrier before casting doubt on whether he can continue at the Australian Open.
Meanwhile Dominic Thiem came from two-sets down to overcome Nick Kyrgios and a Russian known as the Lion roared into round four in a huge upset.
Here, the PA news agency wraps up day five from Melbourne.
Picture of the day
An image for our times. Security had to usher fans off the Rod Laver Arena at 11.30pm, while Djokovic was still playing, after the Victoria government imposed a new five-day lockdown starting at midnight.
Shock of the day
📈 No. 114 in the world🇷🇺 @AustralianOpen qualifier💪 Back from a serious injury🌟 Beats No.8 seed
Aslan Karatsev, making his first Grand Slam main draw appearance, reaches round four in spectacular fashion 👏#AusOpen pic.twitter.com/aLE6VzWd2u
— ITF (@ITFTennis) February 12, 2021
Lion-hearted Aslan Karatsev had never played at a grand slam until this week. But the unknown Russian 27-year-old is now through to the fourth round after a stunning 6-3 6-3 6-3 upset of eighth seed Diego Schwartzman.
Comeback of the day
Thiem looked down and out at two sets down and facing two break points. But in front of a raucous home crowd the US Open champion and third seed somehow came back to knock out Australian bad boy Nick Kyrgios in a cast-iron classic.
Story of the day
Yet all that drama was overshadowed by the sight of world number one and reigning champion Novak Djokovic battling through the pain barrier to defeat Taylor Fritz in five, before admitting his tournament may be over due to a torn stomach muscle.
Stat of the day
90 👑 | 7 🏆
Congratulations @serenawilliams on your 90th #AusOpen victory 👏 #AO2021 pic.twitter.com/2IgJTowiHy
— #AusOpen (@AustralianOpen) February 12, 2021
Serena Williams' victory over Anastasia Potapova was her 90th at the Australian Open. Her first came in 1998, three years before her opponent was born. Feeling old yet?
Bagel not on the menu for Hsieh Su-wei
Bagel? 🥯
Hsieh Su-wei doesn't want one! #AusOpen | #AO2021 pic.twitter.com/WH02jpKg71
— #AusOpen (@AustralianOpen) February 12, 2021
Hsieh Su-wei had lost a set 6-0 in all of her previous three meetings with Sara Errani, which all ended in defeat. But she was not ready for another bagel in their third-round meeting as she won 6-4 2-6 7-5.
Butterfly effect
.@naomiosaka's new good luck charm? 🦋😊#AO2021pic.twitter.com/hk82DKQ9cL
— wta (@WTA) February 12, 2021
Naomi Osaka's win over Ons Jabeur was subject to a small delay when she received a visit from a butterfly. The Japanese star responded by sending a searing forehand winner down the line in the next point.
Quote of the day
Fallen seeds
Women: Veronika Kudermetova (32).
Men: Diego Schwartzman (8), Denis Shapovalov (11), Pablo Carreno Busta (15).
Who's up next?
Britain's last man standing Cameron Norrie has his biggest challenge yet, as a third-round meeting with Rafael Nadal lies in store. Sadly, there will be no crowd to watch it.
Italy
Wales
Switzerland
Turkey
