Judgement day arrives tomorrow for Labor’s last two state governments. While expectations are that results will complete the nationwide conservative sweep (not counting the ACT), one of the two conclusions is a lot more foregone than the other.

The pattern followed for the cycle of state Labor governments that came to power in the late Paul Keating and early John Howard years has been from narrow initial victory to one or more landslide re-elections, followed by a close result as the opposition recovered its competitiveness. Where the governments survived the correction, as they did in New South Wales and Queensland, troubled final terms in office were followed by electoral annihilation.

Such was the frightening precedent for the Labor governments in South Australia and Tasmania, both of which were lucky to survive in 2010.

Facing the voters for the final time under Mike Rann, Labor in SA was soundly defeated on the statewide two-party preferred vote by a margin of 51.6-48.4, but it did a magnificent job of shoring itself up in the seats that mattered most. In Tasmania, the Labor vote plunged by 12.7% to 36.9%, enough to cost it its majority and reduce it to parity with the Liberals on seats.

Then-premier David Bartlett had sworn he would not form a government under such a circumstance, but did not prove as good as his word when it was demonstrated that any arrangement requiring co-operation between the Liberals and the Greens would be unworkable.

According to the recent script, it would seem that both governments are headed for drubbings of historical proportions tomorrow.

That is certainly what the polls have been suggesting for a very long time in Tasmania, which is just as well for a Liberal Party grappling with proportional representation and an effective three-party system in which Labor occupies the centre ground.

Today’s result from Newspoll suggests the Liberals ascendancy has been cemented still further over the course of the campaign, with their vote soaring to a formidable 53%. Labor has sunk to a disastrous 23%, losing support at both ends as the Greens recover from a late-term slump to 16%, while the Palmer United Party appears to have faded despite an expensive and highly visible campaign.

Not for the first time, voting intentions in Tasmania look to be shaped by expectations concerning the result. Labor’s landslide wins of 2002 and 2006 were at least partly fuelled by a distaste for minority government and the certainty that only Labor offered deliverance from it. This time the tables have turned, with the Labor bearing the brunt of hostility towards power-sharing arrangements involving the Greens, especially in the northern half of the state, and polling over time making it graphically clear which way advocates of a decisive result should jump.

The Liberals are also starting short-priced favourites in South Australia, with Centrebet offering just $1.02 on Steven Marshall emerging from the election as premier compared with $13 for Jay Weatherill. However, the striking fact is how well Weatherill’s government is looking when compared with the similarly placed governments of Kristina Keneally, Anna Bligh and Lara Giddings.

Under South Australia’s conventional electoral system, Labor and the Liberals face a neatly symmetrical situation in which Labor will lose its majority if it drops three seats, while the Liberals will gain one of they win six.

While the swing the polls are pointing to looks modest enough, a legacy of Labor’s over-performance in 2010 is that they have a bumper crop of seats to defend on very narrow margins. There are seven seats that will fall to the Liberals on a uniform swing of 3%, and another four with margins of less than 5%. There is also a chance of a bolter coming in from further up the pendulum, most notably the Whyalla-based seat of Giles, where the retirement of popular sitting member Lyn Breuer makes the seat a lot less safe than the 11.9% margin makes it appear.

Furthermore, of the three naturally conservative independent-held seats, the Liberals are extremely confident of gaining Mount Gambier, and at least vaguely hopeful of taking back the Frome, covering Port Pirie and the Clare Valley.

Nonetheless, the electoral terrain in South Australia continues to favour Labor, with much of the conservative vote locked up in extremely safe rural seats.

Liberal nerves will have been frayed by polling published overnight. Galaxy automated phone polls published by The Advertiser found Labor clinging to 51-49 leads in the seats of Mitchell and Newland, which, being Labor’s fifth and sixth most marginal seats, are exactly the seats the Liberals need to win to be confident of a parliamentary majority.

The Australian has also provided a preliminary result from a Newspoll survey that will be published in complete form this evening, and it confirms the impression of a very slight swing in having the Liberals leading 53-47. Barring a late reversal, it appears the Liberals’ fortunes in South Australia will come down to the manner of the swing’s distribution — or failing that, the whim of a small number of independents.