Dublin 1-11 Donegal 1-12, Croke Park
Substitute Ethan O'Donnell supplied the match-winning point in the 58th minute as Donegal qualified for their first ever All-Ireland Minor Football Championship final at Croke Park.
The Tir Chonaill youngsters beat a much-fancied Dublin team by the minimum margin and were helped on their way by John Campbell's first half goal and man-of-the-match Stephen McBrearty's four points from play.
Dublin, who had led 0-5 to 0-1 early on, thought they had turned the screw when an opportunist goal from Jack Burke (46 minutes) and follow-up point from Colm Basquel put them 1-11 to 1-9 ahead.
But Declan Bonner's Ulster champions produced a brilliant response to reel off the final three points of the game through Lorcán Connor, McBrearty and O'Donnell.
It is a hugely significant result for Donegal at Under-18 level. They last reached an All-Ireland minor semi-final in 2006 and can now look forward to facing Kerry in the decider on Sunday, September 21.
McBrearty, younger brother of senior star Paddy, featured prominently in the opening minutes but Dublin moved 0-2 to 0-1 ahead thanks to points from Burke and Aaron Byrne.
They should have been further in front as a number of promising attacks broke down, maintly due to Donegal's tenacity in defence, while the Ulster champions hit three wides.
The play was open and free-flowing with both teams countering at great pace. Registering scores was proving a problem though, with Caolán McGonigle's wayward 16th-minute effort summing up the growing sense of frustration.
However, Conor Kavanagh broke through to end the scoreless spell and Dublin captain Con O'Callaghan followed him onto the scoresheet with a quick-fire brace.
The Dubs' timely spurt sent them 0-5 to 0-1 clear as Donegal struggled to add to Lorcán Connor's early free. It was not for the want of effort and they certainly made the most of an impending purple patch.
Statuesque full-forward Campbell ignited the game in the 23rd minute when he fisted a high ball in from Tony McGlenehan straight to the net. It was an acrobatic effort as he rose with his back to the goal and managed to direct the ball past Eiven Whelan with his right hand.
The goal really lifted the northerners and Campbell soon had them in front for the first time, pointing on the turn and then reading a short kick-out from Whelan to make it 1-3 to 0-5.
Connor landed his first point from play before lively corner forward Chris Sallier responded for the Dubs. But Donegal were now in dominant form and their forwards continued to make the most of the space afforded to them.
Wing back Mulligan joined the attack to land a skyscraper of a point from the right and McBrearty bent over another fine effort to put a goal between the sides at the break (1-6 to 0-6).
Although O'Callaghan missed a '45' in injury-time, Dublin made immediate inroads when Eoghan McHugh strode forward from the throw-in and cut the gap to 1-6 to 0-7.
Donegal's Niall Friel earned himself a black card when he brought down Byrne just outside the large parallelogram and O'Callaghan tapped over the close range free.
Mulligan rifled over his second of the day in response, but Dublin were beginning to find some rhythm in attack again as O'Callaghan won and pointed a free.
Kavanagh had a goal chance blocked and cleared away and Donegal impressively worked the ball downfield, setting up McBrearty for a classy point off his right.
Sallier kept the pressure on at 1-8 to 0-10 - clipping over his second after intercepting a hand pass - before McBrearty's brilliant anticipation kept Donegal's noses in front.
But, in the blink of an eye, Dublin pounced for a vital goal. Basquel's quickly-taken free was flicked into the onrushing Burke's path and he got past goalkeeper Danny Rogers to finish neatly into the empty net.
A Basquel point from close-in nudged the Dubs 1-11 to 1-9 clear until a Connor free at the increasingly populated Hill 16 end made it a one-point game entering the final 10 minutes.
As the tension mounted, Donegal miscued three shots at the posts - including two placed balls from substitute Gavin McBride - and it took that man McBrearty to lob over the leveller in the 56th minute.
Dublin seemed to tighten up at just the worst time and it was Donegal who were showing more composure. O'Donnell flashed his all-important point just over the crossbar after Dublin had failed to clear a monster free dropped in by McBride.
Now behind, Dublin's late search for the equaliser proved fruitless as O'Callaghan had a long range free diverted wide by net minder Rogers in injury-time, and the subsequent '45' - from far out on the left - was missed by substitute Aodhan Fee.
In the end, Donegal deservedly pulled through with their manager Bonner's intelligent use of the bench also a key factor in deciding the outcome of this memorable clash.
DUBLIN: E Whelan; E Murchan, J Mullins, D Monahan; A McGowan, S Clayton, G O’Reilly; A Foley, E McHugh (0-1); C Kavanagh (0-1), C Basquel (0-1), J Burke (1-1); A Byrne (0-1), C O'Callaghan (0-4, 0-2f), C Sallier (0-2).
Subs used: B Howard for Kavanagh (49 mins), D McIlgorm for Foley (55), W Egan for Byrne (57), A Fee for McGowan (59).
DONEGAL: D Rogers; D Monagle, C Gillespie, CKelly; S McMenamin, T McGlenehan, C Mulligan (0-2); N Harley, C McGonigle; S McBrearty (0-4), L Connor (0-3, 0-2f), M Carroll; J Brennan, J Campbell (1-2), N Friel.
Subs used: E O'Donnell (0-1) for McGonigle (20-24 mins, blood sub), C Morrison for Friel (36, black card), O'Donnell for Harley (39), GMcBride for Brennan (47), C Doherty for Campbell (54), C Bonner for Kelly (58).
Referee: Derek O'Mahoney (Tipperary)