While Serena was moving into the next round, US Open champion Dominic Thiem tumbled out after being beaten 6-4, 6-4, 6-0 by Grigor Dimitrov, who reached the quarter-finals of the Australian Open for the fourth time. Naomi Osaka barely advanced, saving two match points and grabbing the last four games to top Garbiñe Muguruza 4-6, 6-4, 7-5.

Two years ago at this tournament, Williams was on the verge of a quarter-final win when she hurt her ankle and ended up losing.

“Well, my first thought was, ‘Not another ankle sprain in Australia’. But I knew immediately that it wasn’t. Then I was more embarrassed than anything. I was like, ‘Oh, my goodness.’ I don’t like falling, Williams said. “But I was fine. I mean, once I realised I didn’t twist my ankle, like at all, I was like, ‘OK, I’m good, let me just get up’.”

Williams, who wore a black T-shirt with “Unstoppable Queen” in capital gold letters to her news conference, moved closer to an eighth Australian Open championship and record-tying 24th grand slam singles title overall.

Her most recent came in 2017, while she was pregnant. On a cloudy day with the temperature in the mid-60s Fahrenheit (high teens Celsius), both Williams and Sabalenka dismissed much in the way of subtlety or nuance.

“I was OK with it, really,” Williams said. “If she wants to play power, let’s go.” These two hit the ball hard, over and over again in Rod Laver Arena, and Williams was barely better. She ended up with more winners, 30-24, and more aces, 9-4, while cranking up her best-in-the-game serve to as fast as 202km/h.

When Williams needed to volley, she did, rather well, claiming 13 of 15 points when she went to the net. More importantly, she covered the court much in the way she did in her younger days, when opponents’ apparent winners were rendered mere fodder for her own strikes.

And she showed no signs of trouble from the left Achilles tendon that hampered her in a US Open semi-final loss in September and forced her to withdraw from the French Open before the second round later that month.

“I’ve worked really hard on my movement. Yeah, I like retrieving balls. I mean, obviously I like to be on the offence, but I can play defence really well, as well,” the 39-year-old American said. “I didn’t think about my Achilles. It’s so good to not think about it. Oh, my goodness.”

Sabalenka – a 22-year-old from Belarus playing in only her second fourth-round slam match – was visibly and audibly frustrated. She frequently would scream after lost points. She spiked her racquet, too.

With the high quality of the match, the only shame was that no fans were there to see it in person. That’s because this was day two of the five-day lockdown imposed by the Victoria state government after some Covid-19 cases emerged at a local hotel. (Any cheering or chatter TV viewers heard at home was being piped in to broadcasters’ feeds).

Williams was waiting for the result of Simona Halep versus Iga Swiatek to see who she would face next. The other quarter-final on that half of the draw will be Osaka against unseeded 35-year-old Hsie Su-wei of Taiwan.

There were two significant surprises in men’s fourth-round action. Thiem – the Australian Open runner-up and US Open champion in 2020 looked physically compromised in loss to three-time major semi-finalist Dimitrov.

Even more unexpected: Dimitrov’s next opponent is Aslan Karatsev, a 27-year-old Russian qualifier who is ranked 114th and first player in a quarter century to reach the quarter-finals in his grand slam debut. Karatsev eliminated 20th-seeded Felix Auger-Aliassime 3-6, 1-6, 6-3, 6-3, 6-4.

Osaka need to dig deep to put out her three-set victory over Muguruza.

The third-seeded Osaka returns to the quarter-finals of a tournament she won in 2019 for one of her three major trophies. Osaka ran her winning streak to 18 matches – a run that included a US Open title in September.

“She’s playing great. Big shots, big serve,” Muguruza said. “That gives her a lot of free points.”

The key moment came when Osaka was serving at 15-40 while trailing 5-3 in the final set. Muguruza could not convert either chance to end things: Osaka delivered one of her 11 aces at 191km/h on the first; Muguruza missed a groundstroke on the second. Fifteen minutes later, the match was over.

The 71st-ranked Hsieh’s 6-4, 6-2 victory over 2019 French Open finalist Marketa Vondrousova made her the oldest woman to make her major quarter-final debut in the professional era.

This is the 38th major for Hsieh, who beat 2019 US Open champion Bianca Andreescu in the second round. The secret to Hsieh’s success? “I try to pretend,” she joked. “I’m only 18 years old.”