After a two-hour contest at Brighton Grammar School on Saturday, former Napthine government staffer James Newbury resoundingly beat upper house MP Margaret Fitzherbert and former Bayside mayor Felicity Frederico to take over the blue ribbon electorate from retiring member Louise Asher.

The victory came amid allegations of branch stacking linked to one of Mr Newbury's key supporters, Brighton branch president Marcus Bastiaan (claims that Mr Bastiaan has denied).

But it also represents a setback for Mr Guy, who earlier this year set an ambitious target to lift his party's female representation in parliament by a further 10 per cent at every election, rising from 27 per cent this year to 37 per cent in 2018, and to almost half by 2022.

"We are at our best when our team reflects a contemporary Victoria; both in gender and broader diversity… and if we want more women in our state parliamentary ranks then we have to get serious," the opposition leader told the Liberal State Council in April.

Brighton was the first Liberal preselection test since the target was announced. Speaking after the event, Mr Guy said: "James was a strong candidate who won through a democratic process, which is the foundation of the Liberal Party."

Mr Newbury, 38, is a former state and federal staffer, who pitched himself to delegates as someone who could add more "firepower" to the parliamentary Liberal team.

While he is a somewhat polarising figure (Tony Abbott's former chief of staff Peta Credlin, for instance, denied him positions with two federal ministers) the final tally gave him 95 votes compared to 44 for Ms Fitzherbert and 34 for Ms Frederico – a result that supporters on all sides concede was "a smashing".

"I am incredibly humbled and honoured to have been preselected by the Liberal Party for the seat of Brighton. I will spend the next two years (ahead of the election) working hard in my local community to gain their trust and confidence," Mr Newbury told Fairfax Media.

The seat of Brighton has been a Liberal stronghold for decades and now sits on a comfortable margin on 9.77 per cent. But internal tensions erupted last month when Ms Asher – who has previously advocated for more women in safe Liberal seats - backed Mr Newbury to replace her, raising the ire of several of her colleagues.

Hostilities broke out again this week, when Mr Bastiaan was accused of stacking new members into the branch in order to sway the vote in favour of Mr Newbury - an allegation Mr Bastiaan described as "false and politically motivated." The matter came to a head on Friday, when an emergency meeting of the party's administrative committee was called to debate the issue, only to decide that all delegates could vote in the preselection as planned.

Party president Michael Kroger congratulated Mr Newbury and said he would make an "outstanding replacement for Louise Asher, who herself had been a brilliant member of Parliament."

The preselection for another safe seat – the electorate of Nepean, being vacated by retiring MP Martin Dixon – will be held in Cape Schanck on Sunday.