On the national stage, the high-profile battle between leader Richard Di Natale, with his centrist approach, and the hard-left NSW Senator Lee Rhiannon looks like it will be fought to the political death.

The fault lines in Batman are familiar: Bhathal's foes are long-term party stalwarts, fellow members of the Darebin branch, aghast at some of the people surrounding the candidate, who they say are newcomers to the party with a "whatever-it-takes" approach to their politics.

This campaign should have been a dream run.

Not even Labor people have fancied their chances of holding Batman against the Greens' rising tide in Melbourne's inner-north, described, by one exasperated ALP operator, as a "juggernaut" driven by the area’s changing demographics.

Once the Liberals decided not to run a candidate, the Greens' Alex Bhathal was assumed to be likely to win at a canter in what will be her sixth attempt at the seat. But Bhathal's most dangerous enemies have proved to operate within her own party.

The dissidents are also unhappy that Bhathal threw her support behind first-time candidate Lidia Thorpe to stand in a state byelection last year over long-term candidate and Darebin local councillor Trent McCarthy.

The fury of some members of the Greens' largest branch was not soothed by Thorpe's subsequent crushing of Labor in its former bastion of Northcote in November, a result that was supposed to have paved the way for the Greens to sweep to victory in the federal division of Batman.

The trouble started well before David Feeney resigned from parliament over his mislaid citizenship papers.

A 101-page dossier of complaint against Bhathal, delivered to state party authorities on or around January 18, alleged the candidate was a bully, a branch stacker and "toxic element in our party".

Feeney was, at that point, in deep strife over his eligibility to sit in Parliament and Bhathal's enemies knew there was a byelection in the air.

In the wake of Feeney's January 31 resignation, a hastily convened party investigation cleared Bhathal of the allegations, which she strongly denies, and Di Natale pointed out the candidate was preselected by the Darebin branch with more than 230 votes for her and just 19 against.

But the complaint was never going to stay buried. There simply was not enough time for a thorough inquiry to be conducted and the ill-feeling ran too deep.

So someone leaked the dossier of complaints to The Australian and the ABC, with the story breaking on March 1.

The Greens’ command-and-control structure kicked in as the party scrambled to limit the damage, with local branch members ordered not to comment and the leadership rallying around Bhathal.

But the initial attack, two-and-a-half weeks before polling day, was deftly timed.

Bhathal has been forced to deny she is a bully at virtually every major media engagement since, and the leaks have kept coming, despite vigorous attempts to shut stories down.

Di Natale himself publicly conceded the campaign was sabotaged from within after some Darebin members briefed journalists, anonymously, that they would rather see the Greens lose the byelection than Bhathal take up the seat in Canberra.

Kearney’s campaign can hardly believe its luck.

But the Greens' brand is so strong in central Melbourne, particularly in the gentrified neighbourhoods in Batman’s south, that Bhathal still stands an excellent chance of taking the seat.

The Greens have successfully turned the screws on Labor over its tortured position on the giant Adani mine proposal in Queensland, exposing Labor leader Bill Shorten’s sometimes farcical attempts to walk both sides of the street on the issue.

Bhathal’s campaign has also had good mileage out of the vexed political issue of asylum seekers, forcing Kearney to repeatedly concede she will toe the Labor line on policies she personally opposes.

The stakes are sky-high for the Greens on Saturday.

They must capture seats such as Batman, and the next-door electorate of Wills, if they are to bring their balance-of-power ambitions within reach.

A win in Batman would generate desperately-needed momentum for a party that underwhelmed in the 2016 election and had a horrible 2017, riven by internal strife and losing two senators to the citizenship saga.

But if Labor can hold onto Batman, it will be hugely encouraged in the struggle to keep its traditional inner-city strongholds and the story of the byelection will be once again be about the Greens' infighting and underperformance.

Under that sort of pressure, people can go to pieces.