Libs sneak into SA by-election lead: count

The battle for the Adelaide seat of Fisher has taken another twist, with the Liberals pulling narrowly ahead.

Liberal candidate Heidi Harris leads Labor's Nat Cook by just 17 votes on a two-party-preferred basis after a further 4650 pre-poll votes were counted on Tuesday.

With just a few hundred pre-poll votes left to be counted, it looks increasingly likely the final result won't be known until Saturday, when final preferences are distributed.

About 24 per cent of people on the Fisher roll voted early or lodged postal votes for Saturday's by-election.

The Liberals were expected to win back the seat, previously held by former Liberal Bob Such, who became an independent in 2000 and died from a brain tumour in October.

But Labor emerged from the initial count with a lead of 628 votes, giving them a swing of more than nine per cent.

Senior Liberals admitted Defence Minister David Johnston's claim he wouldn't trust SA-based shipbuilder ASC "to build a canoe" played a large part in the initial swing towards Labor.

Federal Liberal MP Andrew Southcott said federal issues played a part in the votes, while Assistant Infrastructure Minister Jamie Briggs said the canoe comment was "very, very unhelpful".

Senator Johnston has denied that his remarks influenced the outcome.