Tomorrow’s elections in South Australia and Batman present Labor with distinct challenges: in the former case, asking a fatigued electorate for a four-year advance after 16 years in office; in the latter, holding back a localised Greens tide.

However, a common thread is that Labor finds itself threatened in places it could confidently have regarded as its electoral heartland just a few years ago.

Labor dominated the area of inner northern Melbourne covered by Batman for nearly a century, until its southern end was caught up in the green wave that swept Adam Bandt to victory in the neighbouring seat of Melbourne in 2010. The imperative to these voters during the byelection campaign has yielded an uncomfortable couple of weeks for Bill Shorten, whose balancing act on Adani has succeeded only in alienating both sides.

Now he faces blowback from his newly launched showpiece on dividend imputation, the timing of which suggests it had been pencilled in as a winner so far as the voters of Batman were concerned. If so, it may have escaped Labor’s notice that Batman isn’t quite as young an electorate as the hipster stereotype suggests.

According to the 2016 census, the median age in Batman is 36 — only a shade lower than the national figure of 38, and quite a bit higher than the 30 recorded in Melbourne, the youngest electorate in the country.

Batman actually rates above the national average for persons aged 80 and over, reflecting a cohort that stayed rooted in the community as change swept through it, in many cases enjoying the fruits of soaring house prices along the way.

Now Labor appears to be on the back foot over the issue, with Greens leader Richard Di Natale warning the policy in its present form “could hit struggling pensioners”, and Labor candidate Ged Kearney signalling it could be amended before the next election.

The Greens have had trouble enough of their own, thanks to local party dissidents who have ensured a drumbeat of negative headlines about their candidate, Alex Bhathal. However, accusations of bullying against Bhathal sit oddly with her mild public persona, and despite talk of a late surge to Labor, she has maintained her status as the not-unbackable favourite throughout the campaign.

Meanwhile in South Australia, Labor’s chances of a fifth term are a lot better than they should be, thanks to the apparent dissolution of two-party voting in the state. Not all of this is down to Nick Xenophon and SA-Best — four sitting members are running as independents, at least three of whom look a better than even chance of retaining their seats.

Despite ongoing talk about his diminishing prospects, Xenophon’s campaign has ended with hopeful signs, notably his acclamation as the winner of Wednesday night’s leaders debate. There are also indications that Labor is sweating on SA-Best challenges in some of its traditional northern Adelaide strongholds, despite earlier expectations that the party posed a bigger threat to the Liberals.

A poll conducted on the weekend recorded a statistical dead heat in the seat of Taylor, where Leesa Vlahos is departing in ignominy after her role in the Oakden nursing home scandal, and there are several other Labor-held seats in Adelaide where SA-Best could cause upsets if the stars align just so.

The upside here for Labor is that SA-Best owes these opportunities partly to the weakness of the Liberals, whose candidates SA-Best must outpoll as a first step to defeating Labor on preferences.

This same weakness means the Liberals are once again struggling in Labor-held marginals that are indispensable to their chances of winning a majority.

There is still ample scope for this most unusual election to surprise, with the SA-Best factor ensuring many seats normally regarded as foregone conclusions will be watched closely through the night. But with any SA-Best members likely to be joined by three or perhaps even four independents in a chamber of 47, there seems a strong chance that the state is headed for another hung parliament, followed by an unusually complex game of post-election horse trading.