At first, only one banner can be seen in the Poljud North: black background and white letters roughly translating as 'The swamp that is Croatian football'. Then, as the stand turns grey with thousands holding tiles over their heads, another huge banner is unfolded through the middle. It's a drawing, comic book-style, of a football pitch sunken in green slime with flies gathering around it, surrounded by empty stands and dark clouds. A disturbing spectacle indeed.

But within seconds, everything changes. People start throwing away grey tiles and erecting blue and red ones instead; at the same time, the 'slimy' display is quickly torn down, even ripped apart in places. Amidst the deafening roar of the delighted crowd, another banner unfolds, depicting a clear pitch with many people cheering on the sidelines... Below it, on the fence, the 'Swamp that is Croatian football' message gives way to 'Will be drained out through the power of supporters' movement'. And so the Eternal Derby, one of the fiercest grudge matches in Europe, kicks off.

On the opposite stand, some 200 Dinamo ultras watch in awe, humbled. What they are witnessing isn't anything anti-Dinamo – it's not even immediately pro-Hajduk, but rather a call for unity against a common fiend, against the demons haunting Croatian football. The nation's FA is widely seen as corrupt and rotten to the bone, basking in the national team's glamour while not giving a toss about the league, clubs or fans. Its chairman, the once iconic striker Davor Šuker, is now a much despised figure – but not as much as Zdravko Mamić, routinely described as the 'Puppet master' and the real ruler of Croatian football. He is thought to have power to install managers or break players into the national team.

Incidentally, Mamić is also Dinamo chairman – a man whose reign has brought the Zagreb club seven consecutive domestic titles and financially secured them with around £120 million through player sales and Champions League money. And most Dinamo fans still hate him more than any of their rivals could. Reasons for that are aplenty. Though the club is legally a citizens' association funded by taxpayers' money, it's being run as a family business, with Zdravko Mamić and his brother Zoran (a former Dinamo and national team player, now sporting director at the club) selling off key players every year. Sometimes they make huge personal profits from it, as Zdravko signed 'civilian contracts' with some players in their early development, binding them to share their future income with him. Luka Modrić is one of those – he's required to give up 20 per cent of his salary to Mamić for as long as he's playing professionally; Eduardo is another – the Brazilian-born forward took his case to court and is currently trying to dispute Mamić's rights.

But the thing Dinamo supporters resent Mamić for the most is, the way they see it, robbing their club of its identity. His rule is dictatorial, treating the disapproving club members as enemies and 'mercenaries of the media mafia'. His press conferences are monologues akin to Fidel Castro, where he insults journalists, fans and sometimes rival clubs while shamelessly portraying himself as a martyr – most recently, he revealed that God speaks to him directly and offered to give his liver for the club.

All of that resulted in alienation – not only from the ultras, known as the Bad Blue Boys, the whole supporters' army was affected and Dinamo's 38,000 Maksimir stadium saw a disgraceful average attendance of under 6,000 in this season's Champions League group stage. And the team suffered, managing only a single hard-fought point – their first in two seasons. Meanwhile, the most ardent supporters began organising themselves into the 'Zajedno za Dinamo' (Together for Dinamo) initiative with the sole goal of overthrowing Mamić's dictatorship and establishing democracy at Dinamo – the kind of where all the members would have a say in the club's policies. 'One member, one vote,' became their motto.

The situation at Hajduk Split couldn't be any more different. Plagued by debts that former boards managed to rack up over the years, they've been forced to let many of their key players go for free or at cut-price deals, merely in order to survive. Then they assembled a new squad featuring youngsters from their own academy, with the addition of a few more experienced players who came on free transfers. For the first time in decades – and maybe even in their 101-year-long history – the club entered this season without big expectations.

Nevertheless, the support has been massive and unconditional. The match against Inter Milan in the Europa League qualifying round was the catharsis: a packed Poljud didn't stop cheering and chanting as their boys fought bravely throughout the game, and even as they lost 0-3, they were greeted as winners in the end. At the time of the match, Hajduk were on the brink of bankruptcy and their future looked far from certain, but they found pride in loss and adversity. A large banner saying 'There Is a Light That Never Goes Out' dominated the North Stand. It might sound odd that The Smiths, of all people, would inspire football supporters in a foreign country. But think again: the song quoted is about youth, desperate loyalty and love to death – in this context, it's almost like 'Forever Blowing Bubbles' and 'You'll Never Walk Alone' rolled into one. Reenergised, the squad responded with a little bit of Iron Maiden in the return leg: 'If you're gonna die, die with your boots on' was the attitude as they beat Inter 2-0 at Meazza in a surreal game, with 4,000 away supporters out-voicing the Italians in the stands.

The extremely loyal Hajduk fans, collectively known as Torcida and founded in 1950, are the oldest organised supporters' group in Europe. They're not your average ultras or a firm, their activities spanning much more than making banners, chanting and performing choreographies. It's basically a popular movement, which has been the most constructive force in Hajduk (and, perhaps, in Split) over the last decade.

Unlike Dinamo, Hajduk is a public limited company. The City of Split holds the majority of shares, while the rest belongs to members – a few are local businessmen, but mostly these are supporters who could only afford to buy one share to frame and hang on the wall of their living room, plus one or two for their (in some cases, unborn) children. In order to bring together shareholders and get the club's board democratically elected, Torcida started an initiative called 'Naš Hajduk' (Our Hajduk), which soon gained widespread support. They also outlined the so-called Kodeks (The Code), a set of rules specifying criteria each board member has to meet. Torcida fought for this for two years before managing to get The Code accepted into the club's statute. A new board was elected in late 2011 and immediately started to implement strict austerity measures, with full support from the fans. But Torcida can also show some muscle when needed – in October 2012, when the City withheld its guarantee for a bank loan needed to save the club, because the Mayor was unhappy with the new chairman the board had elected, supporters immediately took to the streets in thousands and besieged the town hall... Fearing riots, the councilmen quickly changed their minds.

'A Hajduk coach can't be afraid, can't be a coward', said Mišo Krstičević, the current gaffer, in the media prelude to the Eternal Derby. 'The players must know that coach is always by their side. Our greatest strength is togetherness'. He stepped on the slippery ground by announcing the game as a battle between the South and the North, but then he explained he only referred to differences in style: 'Teams from the north are good in ball possession, while my team is on the trail of Ivić's Hajduk'. A reference to Tomislav Ivić can still light up a fan's imagination. The legendary coach who died two years ago introduced high pressing, automatism and quick transformation in the 1970's, winning seven Yugoslav trophies with Hajduk and making them a force to be reckoned with in Europe. He also went on to coach several continental giants such as Ajax, Porto, PSG, Atletico Madrid, Marseille and Benfica, winning league titles in five different countries – plus the UEFA Super Cup and Intercontinental Cup with Porto.

As Dinamo traditionally relied on inspiration of their midfield fantasistas (Boban, Prosinečki, Modrić, now Sammir), Hajduk were always more direct and, as such, somewhat in contrast with the typical Yugoslav school of football. The derby used to be about that, a long time ago when both clubs made up the so-called 'Big Four' along with Red Star and Partizan Belgrade. Now there's some of the 'North vs South' element left in their rivalry, but essentially it's a clash between the poor, but free and proud – and the rich, but oppressed and ashamed.

Hajduk are doing better than most had expected from this young squad, holding second position in the league with the same number of points as Lokomotiva Zagreb – who are, for all intents and purposes, Dinamo's farm team. Such is Mamić's influence in the FA that they can get away with it: their 'sister team' use their ground (where they never attract more than a couple hundred spectators) and have no less than 18 former Dinamo players (either on loans or via free transfers) on their roster. The link isn't a secret – the Dinamo bosses have been publicly bragging about it for years and nobody did anything. But a week before the Eternal Derby, the 'Naš Hajduk' filed in an official complaint to the national Agency for protecting the market competition, detailing how Dinamo and Lokomotiva have formed a 'cartel' and urging the institution to take measures.

Eight points separate the eternal rivals. If Hajduk can win the Derby, it would breathe some life into the title race; a defeat would effectively mean Dinamo secured their eighth in a row. That would bring them one step closer to fulfilling Mamić's prediction: upon seizing power at the club, he proclaimed that Dinamo will be champions for the next ten years. But their domination has become something like a bad joke: while they make multi-million transfers and strut their stuff in the Champions League, most of their competitors in Croatia struggle to survive. A few haven't paid wages for months and last season two top-tier clubs went out of business. So when Dinamo celebrate, they do it alone – fans have boycotted title celebrations in recent seasons and the team waved their trophy, drank champagne and enjoyed fireworks at the eerily empty Maksimir stadium. Last year, their ride through Zagreb in an open-top bus mostly attracted the snap-happy tourists. The travesty of it all must hurt Dinamo fans the most, but as long as Mamić is in the club, they don't feel at home there.

On the Poljud pitch, Dinamo look determined to break the spell: despite all their domination, they haven't won here since 2007. But this is nothing like the passing, possession-based game they are traditionally associated with – they play in very shallow formation, aggressively trying to block Hajduk's ball flow in the middle and on the flanks, relying on quick breaks offensively. The hosts look very insecure at the back, as they are missing their first, second and third choice centre-backs, who are all injured and unavailable for selection. Suddenly, Dinamo's 17-year-old Tin Jedvaj makes a brilliant assist from deep to the towering striker Ivan Krstanović and Hajduk defence is caught off guard: 0-1. Torcida only turns up the volume. Hajduk are taking the game to Dinamo, but they lack composure in the final third. However, they somehow manage to draw level as Jozinović's shot from just outside the box is deflected off Josip 'Crazy Joe' Šimunić, the Aussie-born veteran famous for receiving three yellow cards from Graham Poll in a single 2006 World Cup match... But only a minute later, as Poljud was still erupting with joy, Dinamo's Luis Ibáñez' misfired cross spectacularly lands in the net and it's 1-2 at half-time.

In the second half, Dinamo continue with their aggressive challenges. Hajduk players start to feel nervous and hit back, but their hopes are revived as Dinamo's Marcelo Brozović gets a second yellow card. Now the guests sit deep and invite pressure, but the hosts can't get through and look very vulnerable on the counter. And then, some ten minutes from time, Hajduk's substitute Tino-Sven Sušić (nephew of Safet Sušić, the Bosnia and Herzegovina manager) fends off a challenge from Šime Vrsaljko in the Dinamo box, probably fouling him in the process. He finds himself in a clear chance to score, but a Dinamo defender reaches out off the ground and blatantly, deliberately, handballs the shot... The ref doesn't see any of it, giving a corner kick to Hajduk. This is not just Vrsaljko's hand – it's the Hand of the Devil. They've been cheated of points a few times before this season and they can't look any further than Mamić's alleged huge influence on the referees' organisation.

Dinamo supporters will still enjoy teasing their rivals and saying it's in their nature to always bitch about things, but they will also acknowledge that something is seriously wrong in the 'Swamp that is Croatian football'. As much as they dislike their rivals, they crave the same things that Hajduk already have: full stands and great atmosphere, a team made of character players who know the value of the jersey they wear, but above all – it's democracy. For their next match, the Bad Blue Boys prepare a banner saying: 'Freedom for Dinamo'.

And as the players in blue celebrate their away win in Split, the Poljud crowd isn't paying any attention to them. Bound by camaraderie and desperate pride, they still sing – just like they have been throughout the match. 'If you don't become the new champ', they roar. 'Torcida will mourn, will forgive you... Because we all still know that you're the best, and we'll never turn our backs on you...'

There is a sense that something greater is afoot. The road they're taking might be longer and darker than Sveti Rok – the highway tunnel connecting the north and south of Croatia – but they chose to be the light at the end of it. And even their most bitter rivals can find it in their hearts to respect that – because, despite all the success and trophies – they feel the same way.

Follow Aleksandar on Twitter @AlexHoliga.