Tensions in the ALP are set to erupt if the party fails to make any gains in Bill Shorten's home state, with Victorian Premier Daniel Andrews already facing angry recriminations for his handling of the CFA dispute.
As polling booths closed on Saturday evening, Labor was under threat in one of its key Victorian seats - the Chisholm electorate vacated by former speaker Anna Burke - and its initial hopes of winning back the marginal Coalition seat of Corangamite had been dampened by the firefighters' stoush that continued to simmer throughout voting day.
The contest between the ALP and the Greens had also intensified in the inner city, particularly in the seat of embattled MP David Feeney, who was relying on favourable preferences to help get him over the line. 
And elsewhere, in the state's north, Liberal party hardheads conceded the contest for Sharman Stone's former seat of Murray would go down to the wire against the Nationals.
Speaking earlier in the day, Mr Shorten tried to play down the impact of the firefighters' dispute, which exploded mid-campaign when Mr Andrews sought to push through a controversial union deal that led to the resignation of a key minister, the CFA's chief executive and fire officer, and the sacking of the entire CFA board.
Asked if Mr Andrews was invited to his election party, the Opposition Leader replied: "All my state Labor colleagues are completely welcome" before accusing Prime Minister Malcolm Turnbull of "exploiting volunteers as political pawns."
However, federal Labor insiders are privately furious that the CFA stoush had spilled over to such an extent, hindering Mr Shorten's ability to campaign as aggressively on his home turf, and giving the Coalition fresh ammunition to claim that Labor is beholden to unions.
"The CFA stuff started off as white noise, but for the past few weeks it's hurt us in the marginals," one campaign insider told Fairfax Media. "It's fair to say Victoria is looking pretty dire."
In other developments across the state on Saturday:
" Party strategists from both sides said it was unlikely the marginal Coalition seats of Dunkley, Latrobe and Deakin would fall to Labor, despite internal ALP polling leaked on Friday night showing that the party could secure a swing of up to 3.6 per cent in Victoria.
" Four men suspected of links to the Labor Party were arrested after an alleged late-night vandalism spree at polling booths in Melbourne Ports.
" Things turned ugly in the seat of Higgins, when police were called in to investigate claims that a Greens volunteer had been bitten by one of Assistant Treasurer Kelly O'Dwyer's supporters.
" ALP number-crunchers were cautiously optimistic of retaining Victoria's most marginal seat, McEwen, held by Rob Mitchell with an 0.2 per cent margin.
" About 600 members of the United Firefighters Union handed out anti-Liberal voting cards at polling booths in the seats of Deakin, Dunkley, Corangamite, Menzies, Latrobe and Isaacs, in a bid to counter an expected campaign by volunteer firefighters.
After a gruelling two months, the convention wisdom was that Saturday's election would be won in NSW and Queensland, with Victoria - the country's most progressive state - widely seen as fairly safe territory for Labor, which currently holds 19 out of the state's 37 seats.
However, any major losses for Labor are likely to spark internal recriminations in Victoria. While some point the finger at Mr Andrews for giving the Coalition political ammunition, state-based insiders have already sought to blame Mr Shorten, claiming the federal leader demanded that the Premier resolve the issue after the UFU threatened to doorknock the inner-city seat of Wills.
Mr Andrews kept a low profile on Saturday, for the third consecutive day since CFA chief fire officer Joe Buffone resigned earlier this week - the latest casualty since the Premier's intervention in the EBA dispute in   June.
A Labor loss would trigger an automatic leadership ballot under the party's rules. Candidates would have seven days to nominate after the poll, with caucus accounting for 50 per cent of the decision, and the party's rank-and-file accounting for the other half.