The Liberals have withstood a large swing against them to hold on to victory in the South Australian Davenport by-election.

Liberal candidate Sam Duluk claimed victory after Labor candidate Mark Ward conceded defeat.

Labor appeared likely to have secured a swing of more than 5 per cent towards it on a two-party preferred basis, transforming the Liberal stronghold of Davenport into a notionally marginal seat.

Analysts had predicted a swing towards Labor, although not large enough to delivery them a victory.

The by-election was held to choose a successor to longstanding Liberal MP Iain Evans.

In his victory speech, Mr Duluk said it was an honour to take the reins from Mr Evans, whose father Stan had held the seat before him.

"Very big shoes to fill from Iain and Stan, so thank you Iain for your support and Stan as well," he said.

"Thank you to the people of Davenport for showing your trust in me and the Liberal Party, I'm very humbled to be the new member here."

Weatherill welcomes 'extraordinary turnaround'

Labor is also claiming a victory, with Premier Jay Weatherill describing it as a "fantastic result".

"Governments in their fourth term get average swings against them of 20 per cent. They don't get swings toward them so this is an extraordinary turnaround," he said.

The new Liberal Member for Davenport Sam Duluk flanked by predecessors Iain and Stan Evans. ( ABC News: Nick Harmsen )

"There was a swing at the last state election and [we've] almost doubled the swing here at the by-election."

Mr Evans disputed claims the seat he held for more than two decades was now at risk and insisted Mr Duluk had strong community support.

"When you have a 30-year incumbent family leave the seat, you're always going to get a swing against it," he said.

"The reality is we have won the seat 52-48. It's a great result for the Liberal Party and I think this actually strengthens [Opposition Leader] Steven Marshall's position rather than weakens it."

There was controversy surrounding the ballot after Labor election flyers claimed Mr Duluk did not live in the seat.

Mr Weatherill said questions over Labor's election day tactics were "matters for the party secretary".

"There's always a bit of skirmishing. I mean, I think the Liberal Party were engaged in a few sharp practices as well," he said.

Meanwhile, Greens leader Mark Parnell accused the Liberals of trickery by having volunteers in plain clothes handing out how to vote material encouraging voters to place Greens last.