Colaiste Eanna CBS came from behind three times, before blowing away De La Salle College Dundalk to claim their first Leinster Senior Boys Cup title.
The Rathfarnham school were pushed all the way for 60 minutes by their Dundalk rivals - who went down to 10 men midway through the first half - before pulling away in style at the MDL Grounds in Navan.
Division Two Dublin and Leinster league successes last year represented éanna's first success since investing in soccer four years ago, but last Friday's result sent them onto another level.
Underdogs throughout this year's tournament, the capital side will now travel to Waterford in two weeks' time to face the Munster champions in an All-Ireland semi-final.
However, it looked like there was only one team destined to repesent Leinster as Dr Tony O'Neill Cup winners in the national competition as De La Salle raced out of the blocks in the Under-20 decider. Coming in on the back of a recent semi-final victory over last year's winners, Patrician College, the Dundalk school capitalised on having the tip-off by working a goalscoring chance for Shane Gregory inside the opening minute and he made no mistake. Rudi Kinsella struck the crossbar with a reply for éanna, before Warren Egan levelled the scores with a sixth-minute header.
Despite Adam Shields seeing red for a challenge that most agreed resulted in him connecting with the ball, De La Salle retook the lead through Anton Reilly on 26 minutes.
Eoin Stokes levelled again two minutes into the second period before Gregory's stunning free-kick gave De La Salle a third lead.
Adam Kavanagh's immediate response was followed by a smart finish from Eric Healy, before Egan produced a stunning chip with éanna's third goal in less than five minutes. The Dublin intercounty minor footballer from last year completed his hat-trick soon after as the capital side pulled away and substitute Djamell Djedda sent them into seven heaven before the end.
COLÁISTE ÉANNA: Conor Kieran; Darragh Langan (Michael Monaghan 90), Adam White, Luka Lavic, Hugh Keller, David Miley (Craig Canthy 70), Rudi Kinsella (Conor Crowley 73), Eoin Stokes, Warren Egan (Djamell Djedda 75), Aaron Kavanagh, Eric Healy.
DE LA SALLE DUNDALK: Oisín Finn; Adam Shields, Danny O'Brien, Aaron Casey, James Renaghan, Deane Walters, Liam Keenan, Adam O'Connor, Anton Reilly, Robert Mackin, Shane Gregory. Subs: Xheraldo Gorjetta, Jason Quinn, Anthony Lines, Aaron Kelly, Carl Farrell.