An exclusive Mercury/IRIS poll of 400 voters this week shows Mrs Gash is ahead of Labor's Neil Reilly by 58 per cent to 31 per cent in the primary vote, with Greens candidate Ben van der Wijngaart trailing on 11 per cent.

On a two-party preferred basis, Mrs Gash holds a commanding 60-40 lead over Mr Reilly, which would deliver her a hefty 10 per cent margin on August 21 and transform the seat into a Liberal stronghold.

Mr Reilly, who entered the race just three weeks ago after the late withdrawal of former candidate David Boyle, said the daunting results would only firm his resolve.

"In a positive sense it makes you fight harder when it appears you're in a corner; I think we'll just come out fighting," he said.

Doorknocking in Barrack Heights yesterday, Mrs Gash said she would not rest despite the encouraging figures.

"Polls come and go, but people will make up their mind at the ballot box and it will depend how we perform in the campaign," she said.

"I never feel comfortable."

The result will give a boost to the Coalition, which considers Gilmore a must-hold seat if it hopes to form government.

IRIS executive director Simon Pomfret said Mrs Gash's personal popularity and Mr Reilly's tumultuous path to preselection had helped stretch the Liberals' lead.

"Jo Gash has a very high profile, she is the incumbent and she's been around a long time," Mr Pomfret said.

"Neil Reilly's not had a smooth run to be the candidate for Labor, and that's certainly had an impact."

Mrs Gash has an unassailable lead in her traditional Shoalhaven heartland, securing a whopping 67 per cent of the primary vote.

Mr Reilly fared better in the crucial new northern tip of the electorate, polling well in the Labor-dominated suburbs of Barrack Heights, Warilla and Albion Park Rail.