Senior star Cormac Costello kicked the winner as Dublin came from behind to beat Cavan 0-11 to 0-10 and secure their Cadbury All-Ireland U-21 final spot against Roscommon.
The 2012 winners and tournament favourites had to achieve victory the hard way, moving ahead for the first time in the game in the 60th minute when Costello converted a free.
It was a controversial finish too with referee Derek O'Mahoney requiring a Garda escort off the pitch at O'Moore Park.
He applied the advantage rule after Gavin Ivory had initially kicked a Dublin wide, allowing Costello to score the winner.
Minutes earlier, Conor McHugh had levelled the scores at 10 points each with a Dublin point, having been lucky to avoid a black card.
Four-in-a-row Ulster champions Cavan looked set to remain in line for a first ever title at the grade as they led from the first score until the 56th minute.
But three Dublin points in a row in the final seven minutes ultimately secured victory for Dessie Farrell's side and a clash with Roscommon in the final.
Dublin were without long-term cruciate injury victim Ciaran Kilkenny, while senior midfielder Shane Carthy, their Leinster final star, was one of three late withdrawals.
The Dubs were poor early on and blasted nine first-half wides - 14 in total - with All-Ireland senior medallist Paul Mannion and Conor McHugh both errant.
Cavan were more economical in attack and although they didn't create any goalscoring opportunities, they picked off some great scores.
Joe Dillion was their key man at right corner-forward. however, he was substituted late on for a black card offence. He had an epic battle with Dublin full-back David Byrne and kicked three great points from play in the first-half.
Cavan's third score opened up a 0-6 to 0-3 lead after 25 minutes and they moved four clear when Enda Flanagan converted a free.
But Dublin pulled two important points back before the break through Niall Scully and Costello.
Injury doubt Costello showed how much it meant by pumping his fist in celebration as Dublin trailed by just 0-7 to 0-5 at half-time.
Dublin couldn't build on the momentum initially and Cavan reopened their four-point lead early in the second-half.
Dara McVeety played in Thomas Hayes for a point before Flanagan converted another free to leave Cavan 0-9 to 0-5 ahead.
Dublin finally hauled themselves back into contention with three points in a row in the third quarter of the game.
And they provided another trio of late scores in the closing minutes to rob Cavan of their place in the decider.
Dublin: L Molloy, R McGowan, D Byrne, R McDaid, J Small, J McCaffrey, B Fenton. P O'Higgins, E Lowndes, N Scully (0-01), S Boland, N Walsh, C McHugh (0-03), P Mannion (0-01), C Costello (0-04, 2f). Substitutes: E O Conghaile (0-01) for O'Higgins, G Burke for Walsh, G Ivory (0-01) for Boland, Shane Cunningham for Scully.
Cavan: J Farrelly, A Watson, K Clarke, B Fortune, C Brady (0-01), P Faulkner, G Smith, CP Moynagh, L Buchanan, P Graham, D McVeety, M Argue (0-01), E Flanagan (0-02, 2f), J Dillion (0-03), T Hayes (0-02). Substitutes: A O'Hara for Moynagh, Boucher (0-01) for Dillion, Moynagh for Fortune, C Byrne for Flanagan, E Hession for Graham, G McGovern for Buchanan.
Referee: D O'Mahoney (Tipperary).