The Liberal Party is almost 400 votes ahead on a two-party preferred basis in what had been the safe seat of Sturt, in Adelaide's eastern suburbs.
Labor's Sonja Baram was leading by 0.6 per cent (or 890 votes) when counting finished last night, but after counting until 4pm ACST today, Liberal MP James Stevens was 386 votes ahead.
The vote had been neck-and-neck in the morning.
Mr Stevens first won the electorate in 2019 following the retirement of Christopher Pyne.
It had a 6.9 per cent margin in 2019, putting it outside the realm of what is usually considered a marginal seat.
Last night, Ms Baram said voters wanted to be listened to.
"I'm surprised by the swing but I've been working really hard, you know, having one-on-one conversations and when I'm talking to people, they're saying what they want and it is not what the Liberal Party was delivering — absolutely not," she said.
Mr Stevens last night said he believed he had done enough to hold on, despite the big swing against him.
"I haven't won it yet," he said.
"I intend to and hope to win the seat, but I think we'll need to wait a few days before I can properly claim victory."
Boothby win 'very significant'
Labor appears to have won Boothby with a margin of more than 3 per cent, although Liberal Rachel Swift has not yet conceded.
Labor's Louise Miller-Frost leads by almost 6,000 votes with only one polling place yet to have its ballots counted.
Premier Peter Malinauskas said it was a win for his party.
"That's a very significant showing and one that speaks to the culture of South Australian Labor, and regardless of showings and affiliations we get around one another."
