While the Labor Party is expected to easily win the South Australian state election on Saturday, opinion polls show One Nation at 22 to 28 per cent, outpacing the Liberal vote at 14 to 20 per cent.
Flinders University public policy associate lecturer Josh Sunman said One Nation's discipline had been the surprise story of the campaign.
"The fact that we got to the final week and there was only one negative candidate story about One Nation, and that was (candidate Aoi Baxter) was perhaps a fly-in from Sydney, was really instructive to me," he said.
Hours after he made the comment, the ABC reported a UK court had issued an arrest warrant for Mr Baxter over a charge of sexually touching a woman without consent, and he was swiftly disendorsed by One Nation.
Mr Sunman said One Nation had delivered targeted messaging and candidate discipline, and "I was expecting a lot more candidate scandals and meltdowns".
The Liberals, meanwhile, had run a pretty dismal campaign, he said.
"They have to balance taking on Labor with One Nation, who are just eating away their primary, but they haven't been able to advance a coherent campaign narrative," he said.
However, Liberal leader Ashton Hurn had done an admirable job of trying to present a credible alternative premier, Mr Sunman said.
In the final opinion poll, released on Friday, YouGov forecast a 59-41 win for Labor on a two-party preferred basis against both the Liberals and One Nation, a 4.4 per cent swing in its favour.
YouGov's Paul Smith said Labor was set to secure its largest two-party preferred vote in SA history, while the Liberals were on track for 19 per cent, their worst result in any state or federal election since the coalition was formed.
"One Nation's surge to 22 per cent places them second in the state for the first time, with particularly strong support in regional areas," he said.
Federal leader Pauline Hanson said the major parties were worried about the One Nation factor and agreed the election would be a barometer of the party's popularity.
"I've been here for the last week, and at a polling booth now … the on-the-ground feeling is extremely strong," she told radio 2GB on Friday, as someone yelled at her "Pauline Hanson, you're not welcome here".
Adelaide University emeritus professor of politics Clem Macintyre said the rise and rise of One Nation had the potential to create a watershed moment in Australian politics, and the end of two-party politics at a federal level.
"If they do make a breakthrough, they're going to have to work hard to be a more serious and viable alternative government," he said.
"It's more frustration with the major parties … I think we can still say One Nation is a party of disaffected voters."
Mr Sunman said Mr Malinauskas was a dependable performer throughout the campaign, but there were warning signs for Labor.
"Maybe he just comes off as a bit too arrogant sometimes, and there are echoes of the previous (Mike) Rann era."
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