The South Australian Liberals have consolidated their lead in the Bragg by-election, following the counting of the first pre-poll and postal ballots.
At the closing of counting on Saturday, Jack Batty was ahead of Labor's Alice Rolls by little more than 200 votes.
But by Monday afternoon that lead had grown to more than 1100.
With almost 66 per cent of the vote counted, the Liberal candidate was ahead 53.4 per cent to 46.6 on a two-party preferred basis.
The by-election for the eastern suburbs seat was forced by the recent resignation of former deputy premier Vickie Chapman.
In the March state election, Ms Chapman's 16 per cent margin was halved to eight per cent.
Much of that has now been wiped out in another strong performance by Labor, with the party also benefiting through preferences from the Greens.
Greens candidate Jim Bastiras attracted more than 16 per cent of the primary vote, up on the 13 per cent the party managed at the state poll.
About 9000 voters cast either an early ballot or applied to vote by post in Bragg, with about half of those still to be included in the result.
While Labor fell just short of victory, Premier Peter Malinauskas said it was amazing to think Bragg, so long a Liberal stronghold, was now a marginal seat.
"To be able to get a significant swing to us on the back of an even bigger swing a few months ago is something we're very excited about," he said.
"To get so close is a little surprising. But it's also a demonstration of the fact the people of the eastern suburbs have been taken for granted by the Liberal Party."
Mr Batty told said there was no such thing as a safe Liberal seat anymore.
"I've never taken this seat for granted and I never will," Mr Batty told radio 5AA.
"I treated it as a marginal seat throughout this entire campaign."
With the Liberals set to retain Bragg, the opposition will have 16 MPs in parliament's 47-seat House of Assembly.
The Labor government holds power with 27 seats, with the remaining four held by independents.
