It seems like longer than four years ago. On a balmy May evening in Cavan town, Donegal man-child Michael Murphy crashed a ferocious penalty kick against the cross bar, a whistle shrilled and that was that: Dublin were the All-Ireland under-21 football champions.

Jim McGuinness, the Donegal manager, was over to shake hands with Jim Gavin even as the Dublin man was registering his success. The exchange was the height of courtesy. Nobody knew it then but that moment marked the beginning of a period of revolution and incredibly bold thinking in Gaelic football. Tomorrow brings the two men back to the championship sideline for a direct confrontation between two starkly different and equally legitimate visions of Gaelic football and for what might just be the match of this young century.

When the teams left Cavan that evening, Dublin had not won a senior All-Ireland title since 1995 and were developing an unwanted reputation for choking at the semi-final stage. Donegal were utterly off the charts in terms of contention; any reference to that notion belonged to the nostalgia of 1992.

Jim McGuinness's achievement in 2012 was something entirely new in Gaelic football: a group of freewheeling individualists re-imagined as a ferocious collective capable of executing a radical interpretation of the game to such a high level that they were able to reel off successive wins against Cavan, Derry, Tyrone, Down, Kerry, Cork and Mayo to win arguably the deepest All-Ireland in history.

Dublin, meanwhile, broke their semi-final hoodoo under Pat Gilroy against Donegal in 2011 in what was one of the most notorious matches ever played and also one of the most fascinating. Since Dublin defeated Donegal by 0-8 to 0-6, they haven't looked back, winning the titles bracketing Donegal's 2012 triumph under Gilroy and Jim Gavin.

Holding court

This period of football cried out for another showdown between the counties. Everything about their styles and approach is different, starting with the current managers. When Donegal held their media night ahead of the 2012 final, it was already after 10 in the evening when Jim McGuinness sat down with a big gathering of newspaper journalists and held court on every topic put to him for almost an hour.

One journalist said afterwards that he stuck the recording on to listen to on the night drive home because the conversation had been so absorbing – a first and last in the history of those press jamborees.

The peculiar thing about McGuinness is that for all the criticism thrown at his team he has never clammed up, never turned resentful. He has remained above the fray. So has Gavin and Dublin, albeit in an entirely different way. Dublin’s regular 8am briefings are in keeping with the emerging profile of a county side run like a streamlined and ultra-efficient company. Gavin has managed to watch his team play some of the most scintillating attacking football ever seen while exhibiting all the external excitement of a man sitting through a mildly diverting power point presentation on the monthly sales figures.

Last year, Dublin won the final by a point against a Mayo team which did not play well. Tomorrow, they are 1/10 to beat Donegal. Gavin used this year’s league as a demonstration of shock and awe. The country swooned and nothing they have seen yet this summer has broken the spell.

Alarm bells may be ringing faintly in the minds of Dublin supporters reared on grimmer summers. Has the improvement really been so great? Have the Dubs become actually unbeatable? The fascinating thing about Dublin is that beneath the showtime exterior, they are just as much the product of a system as Donegal are. The philosophies aren’t so different.

Donegal, under McGuinness, have sought to wear teams down through relentless defence. Dublin have decided to do the same through attack.

Donegal's tactics are often compared to basketball but elements of Dublin's play mirror the hardwood game also. The full-field zone press, with everyone from Bernard Brogan back working their socks off, belongs to one of the oldest standards in basketball and begs one of the oldest questions: how do you beat the press?

Watch Dublin's first goal against Monaghan and you can see a move honed on the training ground: McCarthy's run from deep, powering on because he knows the return pass is coming, Brogan's v-cut away and back to goal, knowing too that the pass is coming. It is repetition and hard work presented as spontaneous brilliance.

And what of Donegal? Yes, they are the first team to perfect the zone defence but when it comes to basketball references, it is impossible not to think of Donegal without invoking the spirit of the fearless Detroit Pistons team of 1988-90, who came from nowhere to confront the establishment teams with an emphasis on intimidating defence and an unapologetic attitude of doing what it took to win. Their unpopularity obscured the fact that deep down, they were a terrific basketball team.

Just not cricket

It often seems that the same is true of Donegal: even now, there is an abiding notion that they pulled a fast one in 2012 – that what they did just wasn’t cricket.

It is seldom noted that while Donegal’s defensive blueprint was a combination of McGuinness’s tactical excellence and untold hours of work, their counter-attack was and is, by definition, pure spontaneity.

Even before the 2012 triumph, most people in Donegal understood that they were in the midst of a football period that was close to miraculous. They knew then – and are even more keenly aware now – that winning three Ulster titles and (at least) one All-Ireland in four years is something that they may never see again.

That is where the road divides between Dublin and Donegal. There is no doubt but that Dublin will win All-Irelands in the seasons ahead: the question is how many. Even during the the splendour of the Heffernan era, there can’t have been such a feeling of invincibility coursing through the football strongholds of the city.

Tomorrow in Croke Park brings together two remarkable football stories. They say the bookies are always right in the end and this match may go the same way as others, with Donegal buckling under the deluge. But there is a nagging sense that Donegal will not be quite so acquiescent.

Their entire back catalogue under McGuinness has been about bucking expectations and drawing on exceptional internal resolve. The chief intrigue lies in the fact that nobody is quite sure of what Donegal are going to do while the world knows Dublin’s intent. Both sides will take the field with absolute belief. By six o’clock, Gaelic football will seem changed, whatever the result.

A godly summer storm beckons.