South Australia’s Liberal leader says it will be “exceptionally difficult” for his party to win the Dunstan by-election, but has stopped short of conceding defeat in the seat of former premier Steven Marshall.

With about half the vote counted, the numbers so far favour Labor candidate Cressida O’Hanlon over the Liberals’ Anna Finizio, and also show a significant surge in first-preference support for Greens candidate Katie McCusker.

Labor is not claiming victory, but Premier Peter Malinauskas told supporters on Saturday evening that he was “taken aback” to find his party in an “extraordinary position”.

About 27,000 people were eligible to vote in the by-election, which was triggered by the retirement of Mr Marshall from his inner-east Adelaide seat.

Counting of more than 7,000 pre-poll votes will not get underway until Monday.

Speaking to Liberal supporters at a hotel in the electorate, party leader David Speirs told those gathered that the “results tonight are not looking that promising for the Liberal Party”.

Liberal candidate for Dunstan Anna Finizio faces an “exceptionally difficult” challenge, the party’s leader said.(ABC News: Che Chorley)

“Both major parties have seen a fairly significant fall in their primary votes, there’s been a big shift towards the Greens,” he said.

“That’s going to make our pathway to holding this seat exceptionally difficult going forward. There is a pathway to holding this seat but it is a pathway which has a lot of barriers in it and so that’s going to be challenging.

“For that result, I apologise. I am really sorry that it is as difficult as it might be.”

But he said that, with pre-poll votes still to be counted, there was still a chance “we might get over the line in this election”.

Opposition Leader David Speirs with Anna Finizio during the campaign.(ABC News: Che Chorley)

Ms Finizio expressed pride in the way she had conducted her campaign.

“It was the most marginal seat in South Australia and boy did we give it a crack, we gave it a huge crack,” she said.

Mr Marshall retained the seat at the last election on a margin of just 0.5 per cent, with only 260 votes separating the frontrunners on a two-party-preferred basis.

Mr Speirs earlier rejected suggestions a defeat for his party could precipitate a challenge to his leadership, but conceded a Liberal loss would partly be “a judgement on myself as leader of the party”.

Ms Finizio speaks to supporters at the Liberal function at the Robin Hood Hotel.(ABC News: Che Chorley)

Speaking to volunteers at a Labor function on Saturday night, the SA premier was buoyant about his party’s prospects in the seat named after one of its most successful leaders, Don Dunstan.

“Cressida and I are both quite taken aback to be in this extraordinary position,” Mr Malinauskas said.

The premier earlier said Labor was “up against” history, because “history tells us governments just do not win seats off oppositions at by-elections”.

“It hasn’t happened in South Australia since 1908,” he said.

“It seems pretty remarkable that we are on the verge potentially of doing something that hasn’t happened in South Australia for 116 years,” he added later.

Ms O’Hanlon embraces a supporter.(ABC News: Che Chorley)

“When there’s a by-election … people in the community will seek to analyse and digest: ‘What’s the message here? What’s the signal here?’

“I think there’s one message above all else that comes out of the by-election, and that is the people of South Australia, including the people of Dunstan, just want a united team to get on [with] the job of progressing our state.”

Ms O’Hanlon said she could not “express how grateful I am”.

“Tonight, we are in an incredible position and it’s thanks to all of you,” she told the gathering.

Greens candidate Katie McCusker has polled strongly so far.(ABC News: Che Chorley)

Greens candidate Katie McCusker expressed optimism about a strong primary vote, which could in turn influence the broader outcome.

“We’re not here to make up the numbers, we’re absolutely in this to win,” Ms McCusker said.

“We want to represent this community.”

Liberals forced to withdraw ‘inaccurate’ statements

The sometimes acrimonious by-election campaign ended with the Liberal Party being forced to withdraw statements, less than an hour before polls closed on Saturday afternoon, that were found to be “inaccurate”.

An electoral official with ballots during the Dunstan by-election count.(ABC News: Che Chorley)

The Electoral Commission of South Australia (ECSA) said on Friday it was “investigating a complaint” against the party over social media material published in the lead-up to Saturday’s poll.

The ECSA did not elaborate on the content of the material, but on Friday took the unusual step of resorting to social media platform X to ask the Liberals to contact the commission.

Later on Saturday the SA Liberals confirmed, also on X, that the complaints related to statements claiming Labor was “set to introduce a new GP Patient Tax” which would be “bad news for our health system”.

The seat of Dunstan in Adelaide’s inner east is home to about 27,000 eligible voters.(ABC News: Che Chorley)

The Liberals said the electoral commissioner had determined that the material was “inaccurate and misleading to a material extent and in breach of section 113 of the Electoral Act 1985”, and the party retracted both claims.

“I withdraw the above statement and advise that SA Labor have not introduced a new GP patient tax,” the SA Liberal Media account stated in consecutive posts on Saturday afternoon.

Mr Malinauskas said the Labor Party had lodged a complaint because of “concerns regarding the factual accuracy of materials published” by the Liberals, and did not rule out potentially challenging the result of the by-election because of the material in question.

However, he added: “Let’s wait and see what the outcome is of the election.”

“The electoral commissioner had to undertake the extraordinary action of tweeting to the Liberal Party to get them to reply to him,” he said.

Former SA premier Steven Marshall hands out Liberal how-to-vote cards during the Dunstan by-election which he triggered by quitting politics.(ABC News: Che Chorley)

Earlier on Saturday, hours before his party’s statements on X, Mr Speirs said he was “not concerned about that situation” and believed “we’ve done anything wrong”.

“I’m not aware of what the state director has done, in terms of the specifics. I believe there’s been an attempt to look into what he’s [the commissioner’s] referring to so we can get clarity,” he said.

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