Australian Open: Of Serena's no-look shot, Thiem's great comeback

If Serena Williams somehow manages to conjure up another on-the-run, back-to-the-net, no-look, over-the-shoulder shot in her next Australian Open match, a local coronavirus flare-up means there won't be any spectators to react with the appreciative applause and yells that greeted this one.

That's because while Williams was using that bit of magic Friday to help pull off a comeback victory over an opponent who is 20 years younger, the head of the Victoria state government was announcing a five-day lockdown in response to a COVID-19 outbreak at a quarantine hotel.

Competition at the year's first Grand Slam tournament will be allowed to continue, but no fans can attend as of Saturday.

After the pandemic led to the cancellation of Wimbledon, zero fans at the US Open and only 1,000 a day at the French Open in 2020, the government let Tennis Australia admit up to 30,000 daily, 50 per cent of normal capacity.

But not anymore.

A year ago, Williams dropped just three games against Potapova in the first round. But then the American was surprised in the third round, her earliest exit in Australia in 14 years.

This time at that stage, Williams who has won seven of her 23 Grand Slam singles titles in Australia fell behind in the opening set, which Potapova served for at 5-3. But the 2016 Wimbledon junior champion double-faulted five times in that game, including twice on set point.

Williams then trailed 5-3 in the tiebreaker. But she took the next four points, the last on a 21-stroke exchange that ended with Potapova putting a forehand into the net.

Never more so than shortly after Potapova edged ahead again by breaking to begin the second set.

Williams broke right back with the help of a remarkable get on a lob. After somehow putting her racket on the ball and sending it in the right direction, the 39-year-old paused and smiled, assuming the point was over and then laughed upon realising she won the point, because Potapova responded by putting an overhead into the net.

Williams now plays seventh-seeded Aryna Sabalenka, who matched her best Grand Slam showing by reaching the fourth round with a 6-3, 6-1 win over Ann Li.

She's been accumulating them at quite a pace going back to the end of last season: Sabalenka has won 18 of her past 19 matches.

Other women's fourth-round matchups established Friday: three-time Grand Slam title winner Naomi Osaka against two-time major champion Garbie Muguruza, 2019 French Open finalist Marketa Vondrousova against Hsieh Su-wei, and two-time major champ Simona Halep against either reigning French Open champion Iga Swiatek or Fiona Ferro.

No. 8 Diego Schwartzman became the highest-seeded man to lose so far, eliminated 6-3, 6-3, 6-3 by Aslan Karatsev, a qualifier from Russia ranked 114th and making his Grand Slam debut at age 27.

No. 3 Dominic Thiem, who won the US Open in September, appeared to be in real trouble against Australia's Nick Kyrgios in front of a raucous crowd, but came all the way back from a two-set deficit to win 4-6, 4-6, 6-3, 6-4, 6-4. Thiem's fourth-round opponent is No. 18 Grigor Dimitrov, who advanced when Pablo Carreno Busta retired after losing the first seven games.

Karatsev is the first qualifier to reach the fourth round at Melbourne Park since Milos Raonic a decade ago and will meet No. 20 Felix Auger-Aliassime, who defeated No. 11 Denis Shapovalov 7-5, 7-5, 6-3 in an all-Canadian matchup.

In other action, 2020 US Open runner-up Alexander Zverev won in straight sets and now takes on No. 23 Dusan Lajovic, while eight-time Australian Open champion Novak Djokovic met No. 27-seed Taylor Fritz of the United States at night, with the winner going up against Raonic.