Goals from Ciarán Behan and Louis Dignam saw UCD dramatically upset the odds and regain their place in the SSE Airtricity Premier Division at Drogheda United's expense.
Few would have given College a chance when they fell behind to an early Mark Doyle header but the Belfield side were full value for a more-than-merited win at Tallaght Stadium.
The Students will return to the top tier following a three-year absence, with Dignam’s spectacular second-half winner the pick of the bunch.
The first chance of note fell in the 12th minute as Conor Kane found his namesake Keeley in the box but the defender could not steer his header on target.
That was rectified shortly after as Alfie Bates swung a cross in from a deep position and this time Mark Doyle’s flicked effort beat Dara Kavanagh in the UCD goal.
That should have been the impetus for the Premier Division side to take control but instead it was the Students who took command of the encounter.
First, Dignam forced Fynn Talley to tag the ball behind with a shot from distance before Mikey McCullough tested the English keeper’s gloves from range.
There was nothing Talley could do about Behan’s well-struck left-footed free kick 11 minutes from the break, however, after McCullough had been felled on the edge of the box.
Drogs did have a chance as the half drew to a conclusion but Ethan O’Brien scuffed his effort wide after UCD failed to clear their lines.
Good work down the left from Thomas Oluwa presented Andrew Quinn with a chance to strike from distance but his low shot just evaded the far post.
And Dignam had Talley at full stretch from the edge of the box after Hugh Smith unleashed Behan with a mouth-watering crossfield ball just before the hour.
Bates had Kavanagh at his best shortly afterwards as he picked up a pass from Doyle and tested the keeper’s mitts from 20 yards but the Students stopper did enough to turn it behind.
And that proved to be a difference maker as Dignam started and finished a move by way of a precise ball for Hugh Smith before curling wonderfully home from inside the box.
Drogs did have a brief chance late on as Leo Burney got his noggin on the end of a deep cross from Edwin Agbaje but it was no match for Kavanagh.
And Burney got his head to a Brandon Kavanagh free kick in the dying moments but this time he could not steer his effort on target.
The Drogs pushed hard in the closing stages and sub Jago Godden steered a Brandon Kavanagh free into the arms of Dara Kavanagh as the maroon side sought a lifeline.
And the Louth side had a valid complaint for a potential penalty as Doyle shot appeared to strike the hand of Harry Curtis but his protests were waved away by ref Paul McLaughlin.
Then Dara Kavanagh did brilliantly to steer away a Keeley header in the very last minute of normal following another terrific Brandon Kavanagh ball.
That did not deter the Students, who continued to push for a clincher in injury time and McCullagh was a whisker from deceiving Talley.
The insurance goal was not required, nevertheless, as UCD secured promotion.
UCD: Dara Kavanagh; Luca Cailloce, Carl Lennox, Harry Curtis, Seán Murphy; Mikey McCullough, Adam Wells, Louis Dignam; Ciarán Behan, Sam Norva (Mohan, 75), Hugh Smith.
Drogheda United: Fynn Talley; Andrew Quinn (Anceli,n 74), Conor Keeley, Leo Burney; Edwin Agbaje, Ethan O’Brien (Farrell, 68), Alfie Bates (Godden, 81), Conor Kane; Brandon Kavanagh, Thomas Oluwa (Brennan, 81), Mark Doyle.
Watch the Club Orange FAI Cup final, Derry City v Waterford FC, on Sunday from 2pm on RTÉ2 and RTÉ Player. Follow our live blog on RTÉ.ie/sport and RTÉ News app and listen to live commentary on Sunday Sport on RTÉ Radio 1