The five-day, state-wide lockdown starting at midnight local time to combat an outbreak of the highly infectious UK strain at an airport hotel, is just the latest setback for the troubled tournament.
The year’s first Grand Slam, which started three weeks late to allow international players to quarantine, has already welcomed tens of thousands of socially distanced fans in the biggest crowds seen in tennis since the pandemic.
Under the new measures, some five million people in Australia’s second-biggest city will have to remain at home for five days from midnight, except for a limited number of permitted essential activities.
“These restrictions are all about making sure that we respond appropriately to the fastest-moving, most infectious strain of coronavirus that we have seen,” said state Premier Daniel Andrews.
“I am confident that this short, sharp circuit-breaker will be effective. We will be able to smother this. We will be able to prevent it getting away from us.”
The latest outbreak, stemming from an airport hotel housing international travellers in mandatory quarantine, has so far infected 13 people, including staff and their families.
It has triggered the third lockdown in Melbourne, which came out of a four-month period of isolation in late October and has since remained virtually virus-free.
Tournament director Craig Tiley gave assurances that the Australian Open would continue, with players deemed essential workers and exempt from the lockdown.
“Play will continue. The players will compete in a bubble form,” Tiley said.
“The players have all been very good about it. They understand. They have been through a rigorous programme already,” he added.
The problems at the Australian Open, the biggest international sports event so far this year, underline the difficulties of holding the much more complex Tokyo Olympics, which are due to start in July after a year’s delay.
Play at six warm-up tournaments in Melbourne was also suspended for a day last week when a worker tested positive at one of the official hotels.
Williams: ‘It’s rough’
American star Serena Williams only learned of the new measures when she came off court after her 7-6 (7/5), 6-2 third-round win over Russia’s Anastasia Potopova.
“It’s rough. It’s going to be a rough few days for everyone,” said the 23-time Grand Slam singles champion.
“It’s not ideal - it’s been really fun now with the crowd back. But at the end of the day we have to do what’s best.
“Hopefully we’ll be all right.”
Players also stayed in a "bubble" environment at last year’s US Open in New York, which went ahead behind closed doors, and the delayed French Open. Wimbledon was cancelled for the first time since World War II.
“It’s a tough one,” said Spanish two-time major-winner Garbine Muguruza, after her 6-1, 6-1 win over Zarina Diyas.
“I’m happy that the tournament is going to go on. I’m sad, of course, that the crowd will not be there for the next few days. Hopefully after we will have (that) again.”
The latest announcement comes just as the tournament was showing signs of life, following a tepid start with attendances well below even their reduced-capacity maximum.
Australian showman Nick Kyrgios, who won in front of a raucous John Cain Arena on Wednesday, faces US Open champion Dominic Thiem in an evening programme that is fans’ last chance for live action until next week.
Defending men’s champion and world number one Novak Djokovic, an eight-time winner at Melbourne Park, plays Taylor Fritz in the late match on Rod Laver Arena, the centre court.
However, spectators may face a scramble to be home before Melbourne’s lockdown starts at midnight, with play frequently continuing into the early hours.