The hearing will decide whether the Australian Open's top seed and defending champion can retain his title and become the first male player in history to win 21 Grand Slams.
Novak Djokovic's lawyers painted Australia's effort to deport him as "irrational" and "unreasonable", in an eleventh-hour bid to reinstate the tennis star's visa and allow him to remain in the country to defend his Australian Open crown.
With just hours to go before the first ball is served at Melbourne Park on Sunday, Djokovic's high-powered legal team kicked off an emergency appeal in Australia's Federal Court.
His lawyer Nick Wood sought to systematically dismantle the government's central argument that Djokovic's anti-vaccine views are a public threat and could cause "civil unrest" unless he is deported.
Despite the 34-year-old being unvaccinated, Wood insisted he has not courted anti-vaxxer support and was not associated with the movement.
The government "doesn't know what Mr Djokovic's current views are", Wood insisted.
Government lawyer Stephen Lloyd said the fact that Djokovic was not vaccinated two years into the pandemic and had repeatedly ignored safety measures -- including failing to isolate while Covid-19 positive -- was evidence enough of his views.
"He's chosen not to go into evidence in this proceeding. He could set the record straight if it needed correcting. He has not -- that has important consequences," the government said in a written submission.
Lloyd also pointed to a series of protests already sparked by Djokovic's arrival in Australia.
Those competing arguments will be weighed by a panel of three court justices, who are expected to give their verdict on Sunday, or at the latest on Monday.
Because of the format of the court, their decision will be extremely difficult to appeal by either side.
If the Serbian star loses, he will face immediate deportation and a three-year ban from Australia -- dramatically lengthening his odds of winning a championship he has bagged nine times before.
'We stand by you'
If he wins, it sets the stage for an audacious title tilt and will deal another humiliating blow to Australia's embattled prime minister ahead of elections expected in May.
Scott Morrison's government has tried and failed to remove Djokovic once before -- on the grounds he was unvaccinated and that a recent Covid infection was not sufficient for a medical exemption.
A lower circuit judge ruled that officials at Melbourne airport made procedural errors when cancelling his visa.
For a few days, Djokovic was free to train before a second visa revocation and a return to a notorious Melbourne immigration detention facility.
Many Australians -- who have suffered prolonged lockdowns and border restrictions -- believe Djokovic gamed the system to dodge vaccine entry requirements.
Experts say the case has taken on significance beyo nd the fate of one man who happens to be good at tennis.
"The case is likely to define how tourists, foreign visitors and even Australian citizens view the nation's immigration policies and 'equality before the law' for years to come," said Sanzhuan Guo, a law lecturer at Flinders University.
The case has also been seized on by culture warriors in the roiling debate over vaccines and how to handle the pandemic.
Australia's immigration minister Alex Hawke has admitted that Djokovic is at "negligible" risk of infecting Australians, but argued his past "disregard" for Covid- 19 regulations may pose a risk to public health and encourage people to ignore pandemic rules.
The tennis ace contracted Covid-19 in mid-December and, according to his own account, failed to isolate despite knowing he was positive.
Public records show he attended a stamp unveiling, a youth tennis event, and granted a media interview around the time he got tested and his latest infection was confirmed.
Serbian President Aleksandar Vucic on Friday accused Australia of "mistreating" the country's biggest star, and a national hero.
"If you wanted to ban Novak Djokovic f rom winning the 10th trophy in Melbourne why didn't you return him immediately, why didn't you tell him 'it is impossible to obtain a visa'?" Vucic said on Instagram.
"Novak, we stand by you!"
'With or without him'
Djokovic is currently tied with Roger Federer and Rafael Nadal with 20 Grand Slam titles each.
Spanish great Nadal took a swipe at his rival on Saturday as players complained the scandal was overshadowing the opening Grand Slam of the year.
"The Australian Open is much more important than any player," Nadal told reporters at Melbourne Park.
"The Australian Open will be a great Australian Open with or without him."
Defending Australian Open women's champion Naomi Osaka called the Djokovic saga "unfortunate" and "sad" and said it could be the defining moment of his career.