It may only be an opinion poll, but this week’s state Newspoll result from South Australia must surely have been an Australian first: a poll showing a “minor” party with a primary vote higher than either of the majors.

The poll credits Nick Xenophon’s SA Best with the support of 32% of its 800 respondents, compared with 29% for the Liberals and 27% for Labor.

Furthermore, Xenophon himself — who has abandoned the Senate to contest the Liberal-held seat of Hartley in Adelaide’s eastern suburbs — was streets ahead of his rivals as preferred premier, recording 46% against 22% for Premier Jay Weatherill and 19% for long-suffering Liberal leader Steven Marshall.

Fascinating though it is to see Xenophon’s party in first place, the result is by no means an outlier — a Galaxy Research poll conducted for the Australian Bankers Association two months ago had SA Best at 30%, just one point behind the Liberals and four ahead of Labor.

To consider how such a result might play out in terms of seats under preferential voting, it must be recognised that non-radical third party candidates need only outpoll one of the two major parties to win on the preferences of the other, unless the leading major party candidate either approaches or exceeds 50% of the primary vote (notwithstanding unlikely suggestions that Labor and Liberal might direct preferences to each other, in the manner of big business oligopolists colluding against a new competitor).

With statewide voting figures such as those suggested by Newspoll and Galaxy, it’s difficult to identify more than a handful of seats where this wouldn’t happen.

The big question now is whether this can be sustained through to an election to be held on March 17.

Gambling odds are against Xenophon but this scepticism seems to be based on nothing deeper than a conservative instinct that hasn’t done the art of electoral prognostication too many favours over the past few years.

Certainly Xenophon faces challenges in co-ordinating a fledgling campaign machine and assembling a disciplined team of candidates, but he’s faced difficulties in both areas in the past (particularly the latter) without suffering lasting electoral damage.

Some may object that One Nation was unable to live up to comparable levels of hype before recent state elections, but this is actually only true of Western Australia.

Despite its failure to win more than one seat in Queensland, One Nation’s support was much as polls were suggesting it would be for months in advance, once its failure to contest a third of the seats is taken into account.

Furthermore, Xenophon has a breadth of appeal on his home turf beyond anything One Nation can touch, in Queensland or anywhere else, and he will present a far more credible public face for his party’s campaign than his already forgotten One Nation counterpart in Queensland.

It must of course be recognised that three months is a long time in politics, and a lot may indeed go wrong as Xenophon takes on the institutional power and organisational experience of the major parties.

But if the polls are even half right, Xenophon can lose a lot of skin between now and polling day and still achieve a result that demolishes a century’s worth of accumulated assumptions about the permanence of Australia’s two-party hegemony.