All competition at six Australian Open tuneup events scheduled for Thursday was called off after a worker at one of the tournaments' Melbourne quarantine hotels tested positive for COVID-19.
Players preparing for the year's first Grand Slam tournament, which is supposed to begin Monday, must isolate at their hotels until they test negative for the illness caused by the coronavirus.
"We will work with everyone involved to facilitate testing as quickly as possible," Tennis Australia said in a statement announcing the postponement of all matches that were to be played Thursday at Melbourne Park.
Victoria state premier Daniel Andrews said he called a late-night news conference Wednesday to announce the case "through an abundance of caution," although he did acknowledge new restrictions could impact hundreds of people associated with the Australian Open.
Andrews spoke before all of Thursday's play was postponed, which he acknowledged was a possibility. But as for the Australian Open, Andrews said: "At this stage, no impact on the tournament proper."
Any players, coaches or officials who quarantined at the Grand Hyatt hotel in Melbourne were deemed to be casual contacts of the 26-year-old infected man and required to remain in their hotels until they test negative.
Everyone in the city will be required to wear masks while indoors.
The hotel advertises it has 550 rooms, including 25 premium suites, so potentially hundreds of people associated with the tournament could be forced back into isolation. That could test the resolve of players who have recently come out of two weeks in quarantine, and give ammunition to critics of the decision to allow people to fly in from all over the world for the year's first major.
Australian Open organizers didn't immediately have details of how many players would have to isolate.
Under the current plans, up to 30,000 spectators are expected daily at Melbourne Park for the two-week Grand Slam event and there was no immediate indication of a change.
Everyone who arrives in Australia must undergo a mandatory 14-day quarantine under the COVID-19 pandemic regulations. The Australian Open used three hotels in Melbourne for the bulk of the players to quarantine and had other secure accommodation and facilities in Adelaide, South Australia state, for some of the biggest stars, including Serena Williams, Naomi Osaka, Novak Djokovic and Rafael Nadal.
Players were tested every day during quarantine and weren't allowed to leave their hotels without a negative result.
The infected worker tested negative on his last day at the hotel on Jan. 29, but subsequently tested positive and has been working with government and health officials on contact tracing. Andrews said the man was in a medical facility and dozens of his close contacts were in mandatory isolation.
"This is one case. There's no need for people to panic," Andrews said. "There's no need for people to be alarmed. We Victorians know what to do, and we have proven, as a state, very successful at managing these sorts of outbreaks, these sorts of issues."
Earlier Wednesday, Victoria health officials announced that the state had gone 28 days without a case involving local transmission.
Australia has 909 deaths attributed to COVID-19, including 820 in Victoria state. Most of those were during a second deadly wave last year when a hard lockdown and overnight curfews were put in place in Melbourne.
Just hours before the government's announcement of the positive test, 23-time major champion Serena Williams beat Tsvetana Pironkova 6-1, 6-4 to advance to the quarterfinals of the Yarra River Classic.
Williams will next face Danielle Collins, who upset third-seeded Karolina Pliskova 7-6 (5), 7-6 (3), and could reach a semifinal match against Ash Barty. The top-ranked Barty beat No. 52-ranked Marie Bouzkova in three sets and will next play Shelby Rogers.
Williams was asked when was the last time she played a warmup tournament so close to a major.
Last year's U.S. Open was her short answer. Then she elaborated.
"But before that, before this whole pandemic, I could count the times on one finger I've done that," she said. "I'm just happy to be out here in any circumstances. It's so cool after what the world went through the last 12 months."
Williams had a tough win over Pironkova in last year's U.S. Open quarterfinals, and then withdrew from their scheduled second-round match at the French Open because of an Achilles injury.
Williams won her last major title at the 2017 Australian Open, when she was pregnant with her daughter, Olympia. She's still chasing Margaret Court's all-time record of 24 Grand Slam singles titles, and an eighth in Australia.
On the bottom half of the draw, defending Australian Open champion Sofia Kenin rallied from a set and a break down to fend off Jessica Pegula 5-7, 7-5, 6-2.
Italy and Russia were the first teams to reach semifinals of the ATP Cup, the 12-team men's event.
Fabio Fognini beat Benoit Paire before Matteo Berrettini defeated Gael Monfils 6-4, 6-2 to clinch Italy's win over France, giving the Italians top spot in Group C.
Daniil Medvedev secured Russia's win over Japan when he beat Kei Nishikori 6-2, 6-4. Russia is on top of Group D with wins over Argentina and Japan.
Germany opened with a win over Canada, with Alexander Zverev clinching it by holding off Denis Shapovalov 6-7 (5), 6-3, 7-6 (4), and Australia beat Greece 2-1.
OSAKA IN THREE
U.S. Open champion Naomi Osaka advanced in the Gippsland Trophy with a 3-6, 6-3, 6-1 win over No. 371-ranked Katie Boulter. Next up for her will be Irina Begu, who upset fifth-seeded Johanna Konta 4-6, 7-6 (10), 7-6 (4).
Second-ranked Simona Halep had a more straight-forward 6-2, 6-4 win over Laura Siegemund.
Also advancing were third-seeded Elina Svitolina, who beat former French Open champion Jelena Ostapenko 6-7 (4), 6-3, 6-2, and No. 7 Elise Mertens.
CHAMPIONS IN GRAMPIANS
Three-time major champion Angelique Kerber took a while to adjust in her first match since leaving quarantine, beating Katerina Siniakova 6-3, 4-6, 6-3 in the Grampians Trophy tournament.
It's the event for those players who were forced into hard lockdown — not allowed to leave their rooms, even for practice — after being deemed close contacts of passengers on their flights who tested positive for COVID-19 after arriving in Australia.
Other major champions in the draw included Sloane Stephens and Svetlana Kuznetsova, who both lost in the first round.