Nick Xenophon has refused to declare which party he would support in the event of a hung Parliament.
"That's a hypothetical, I won't answer hypotheticals," he said during a victory party in Adelaide at 8pm, just as election analysts were declaring such an outcome increasingly likely.
Earlier supporters watching the election broadcast at the Palace Cinema in downtown Adelaide erupted in cheers when Mr Xenophon entered the room with Rebekha Sharkie, who was earlier declared the winner in the seat of   Mayo, which had been held by her former boss, the Liberal Party's Jamie Briggs. 
She became the Nick Xenophon Team's first lower house member.
Mr Briggs conceded via a Twitter message. "After a tough fight tonight hasn't been our night, thanks to those who supported me and my best to the new member, it's a great electorate," he wrote.
Asked who she would support in a hung Parliament, Ms Sharkie said she believed such an outcome was unlikely.
Mr Xenophon said he was pleased with his team's progress and that it would provide a base to build from in order to further challenge the electoral dominance of two major parties.
At the time of writing, it appeared likely the NXT would take at least three Senate seats, as well as Ms Sharkie's in the lower house.
He said the NXT - which will soon be renamed - would use its presence in the upper house to pursue reforms, with an emphasis on support for manufacturing, reforms of gambling laws, the strengthening of whistleblower laws and the creation of a federal version of the NSW Independent Commission Against Corruption.
About 9pm, the NXT had secured a swing of over 20 per cent, draining support from both major parties. The crowd at the NXT's election night party included former members of both the Labor and Liberal parties.
Stirling Griff, second on the NXT's senate ticket, said the party's internal polling showed about 20 per cent of people that once voted Labor in SA had moved to the NXT in the lower house and 15 per cent of Liberal voters.
In the Senate, 27 per cent of former Labor voters had switched support and 18 per cent of Liberal voters. "They are really sick of the bickering that is going on between the two of them," Mr Griff said. "What is really significant is the negative advertising campaign that Labor has been running against us."
He said polling suggested NXT support was actually boosted by Labor's negative advertising.
Mr Griff said the party also benefited from Mr Xenophon's reputation. "We play fair, people know that, he has never gone out and attacked candidates. People have had enough of this whole toxic set up between the two major parties."
Both parties have criticised Mr Xenophon for refusing to declare which one he would support in the event of a hung Parliament, and for taking advantage of his minor party status by supporting populist causes rather than taking hard decisions.
In a signal that the Prime Minister appreciated the scope of the threat posed by Mr Xenophon, Malcolm Turnbull targeted him during his final campaign speech earlier this week.
"This threat is real. So when it comes to the minor parties - be they Lambie, Xenophon, Lazarus or Hanson - Australians need to consider very carefully the impact on practical policy outcomes, and the workability of the Parliament," he said.
As results started coming in, Foreign Minister Julie Bishop said, "I seriously don't understand it, because Nick, himself, can't deliver anything.
"He can't deliver a budget. He can't deliver debt relief. He can't provide any policies that would be implemented.
"So I guess it's a protest vote."
Thanking candidates and volunteers Mr Xenophon said the NXT had successfully broken the duopoly of the major parties despite a savage campaign waged against it.
"There is real space in the political centre in this country. Millions of Australians feel left out by the major parties and we are here to fill this void."