Gary O'Neill headed an injury-time winner to give Sporting Fingal a dramatic 2-1 victory over Sligo Rovers in the FAI Ford Cup Final at Tallaght Stadium.
Sligo had taken the lead through Eoin Doyle on 57 minutes, when the midfielder fired home from close-range.
Colm James equalised on 82 minutes from the penalty spot after Sligo goalkeeper Ciaran Kelly had fouled Sporting striker Eamon Zayed.
Liam Buckley's side completed a remarkable comeback in the dying seconds when O'Neill headed home Robert Bayly's cross at the far post.
The victory completes a great week for a club only in their second season, as they also secured promotion to the Premier Division on Monday by beating Bray Wanderers.
Sligo, who were chasing their third cup win, will know they had the chances to put the game beyond Sporting late in the second half, but failed to take them.
However, it will be Sporting that will be representing the League of Ireland in the Europa League next season. The win will also be a massive boost to their attempts to increase their appeal in the Fingal region.
For the neutral, the game provided drama that was a welcome distraction from the international farce of midweek. It may not have been the best FAI Cup final, but it was a keenly contested game in front of 8,105 enthusiastic fans.
Both sides made light of the difficult, blustery conditions at the south Dublin venue and tried to play possession football, which they have become known for this season.
Sporting showed their attacking intent early on as top scorer Byrne and O'Neill fired efforts at Ciaran Kelly's goal, the latter following good approach play by Shaun Williams and Eamon Zayed
Sporting's three-man central midfield of Williams, Bayly and man-of-the-match Shane McFaul had more possession, but Sligo showed early promise out wide and it was from there that their first chance came.
Doyle's back heel found the overlapping Joe Kendrick and he crossed for Matthew Blinkhorn, but the striker sent his header wide of Darren Quigley's left post.
The game livened up on the half hour as Byrne struck the base of the post with a free-kick after Kendrick had tripped Bayly on the edge of the box.
As Sporting pressed, the Sligo defender was then booked for a foul on the pacy Byrne and they had a penalty appeal turned down for handball against Sligo captain Danny Ventre.
At the other end, Lorcan Fitzgerald denied Rafaele Cretaro an opening goal as the defender blocked his goal-bound effort.
The second half began with rain driving in off the Dublin Mountains, as Cretaro and Brian Cash drew saves from Darren Quigley within a minute of the restart.
Sporting brushed off that scare and created a chance of their own as Fitzgerald burst through but a last-ditch tackle from Gavin Peers forced a corner.
Fitzgerald showed his worth at the other end when he nicked the ball away from Blinkhorn after Quigley could only parry a Cretaro shot. Sligo were the dominant side at this stage and took the lead through Doyle on 57 minutes.
Romauld Boco advanced down the right and played a one-two with Blinkhorn before picking out Cretaro. Shaun Maher managed to block Cretaro's effort shot on the line but Doyle pounced to bundle ball over the line.
Byrne had a quiet second half but he created a glorious chance for Zayed with 12 minutes to go. The winger controlled Bayly's cross-field pass and whipped in a cross that Zayed could only bundle wide.
Sporting were pushing for an equaliser and so were always prone to the counter attack, but Sligo failed to add to their advantage as substitute Owen Morrison fired over from ten yards.
They were punished for that missed chance on 82 minutes as James brought Fingal level from the penalty spot.
Alan Keane failed to deal with Williams' long ball and Kelly upended the advancing Zayed. James coolly converted the kick to the delight of the sporting bench and supporters.
O'Neill then snatched victory as it seemed the game was heading for extra-time. Bayly escaped from Boco to pick out O'Neill and he nodded past a stranded Kelly.
Sligo Rovers (4-4-2): 1 Kelly; 2 Boco, 4 Peers, 5 Keane, 3 Kendrick; 6 Ventre, 7 Cash (14 Morrison '56), 8 Ryan, 11 Doyle; 9 Blinkhorn, 10 Cretaro (17 Meenan '70).
Subs not used: 12 Turner, 15 Marshall, 18 Rafter, 19 Camano, 22 Schlingermann.
Booked: Kendrick, Cretaro.
Sporting Fingal (4-3-3): 1 Quigley; 2 James, 5 Maher, 6 Paisley, 3 Fitzgerald; 4 Williams, Bayly, 11 McFaul; 8 Byrne, 9 O'Neill, 10 Zayed.
Subs not used: 12 Whelan, 14 Gannon, 15 Frost, 16 Dawson, 17 Doyle, 18 Kirby, 20 Konopka.
Referee: Alan Kelly