Nick Xenophon is on track to win his seat in the South Australian Parliament and SA Best candidates are favoured to unseat Tourism Minister Leon Bignell and Labor backbencher Nat Cook, a new poll shows.

The telephone poll of 1,051 voters was conducted between January 11 and 14 by polling firm YouGov Galaxy for the corporate sector.

The poll gave Mr Xenophon a strong lead in his quest to seize the north-eastern suburbs seat of Hartley, with 37 per cent of voters intending to direct their first preferences to the SA Best leader.

Incumbent Liberal MP Vincent Tarzia was on 32 per cent, while Labor's candidate, former minister Grace Portolesi, trailed on just 21 per cent.

According to YouGov Galaxy's calculations, Mr Xenophon would hold a 57-43 lead on a two-party-preferred basis.

But the pollster warned that a deliberate strategy by the major parties to preference each other ahead of SA Best would produce unpredictable outcomes.

The poll showed SA Best's lead was even stronger in Mr Bignell's seat of Mawson, with the fledgling party's candidate Hazel Wainright polling 38 per cent of primary votes.

Mawson, which covers much of Fleurieu Peninsula and Kangaroo Island, was significantly redrawn in 2016 in order to give the Liberal Party an odds-on chance of seizing the seat.

Nick Xenophon with more of his SA Best candidates, Carolyn Martin (L) and Kate Bickford (R). ( ABC News: Isabel Dayman )

But the poll showed Liberal candidate Andy Gilfillan polling just 25 per cent of primary votes, ahead of Mr Bignell on 22 per cent.

The poll also showed first term Labor MP Nat Cook faces a re-election challenge in the southern suburbs seat of Hurtle Vale.

Thirty-three per cent of voters surveyed in the seat intend to direct their first preference to SA Best candidate, teacher Michael O'Brien.

Ms Cook polled 29 per cent of first preference votes, while Liberal candidate Aaron Duff polled 23 per cent.

Emeritus Professor Dean Jaensch from Flinders University said he was not surprised by the opinion poll finding.

"Especially as Leon Bignell's seat is very marginal indeed — in fact it slipped over to the Liberal side after the redistribution," he said.

"Nat Cook is also in a very marginal situation so we're talking about two marginal seats, and Nick Xenophon's attempt to win Hartley, so I'm not surprised by that result at all."

NXT still strong in Mayo

The YouGov Galaxy poll showed federal Nick Xenophon Team MP Rebekha Sharkie was on track to retain her seat of Mayo, despite ongoing questions about her citizenship.

The poll of 350 voters in Mayo showed 37 per cent of voters would direct their first preference to Ms Sharkie, ahead of the Liberal Party on 33 per cent and Labor on 18 per cent.

Assuming preferences flowed in a similar way to the 2016 federal election, Ms Sharkie would hold a 59-41 lead on a two-party-preferred basis.