It is a long time since the fans of Shamrock Rovers have celebrated a victory with such vigour.
Supersub Karl Sheppard turned this quarter-final replay on its head with a late brace to destroy Dundalk's treble dream and keep the Hoops' hopes of a 25th FAI Cup win alive.
Pat Fenlon's charges trailed at the break and looked in real trouble at Oriel Park until the introduction of Sheppard prompted a turnaround which stunned the natives and their manager Stephen Kenny.
He will have to pick up his side quickly ahead of Saturday's rematch in the EA Sports Cup final, which should be a spicy affair. Rovers know they have the power to have a big say in a Dundalk season which had pretty much gone to plan until this point, and they enjoyed this moment.
This was a comfortably better game than Friday's initial meeting, although unfortunate TV viewers will know that doesn't set the bar too high.
Dundalk had started the brighter before Rovers succeeded in applying pressure higher up the park as the half progressed. It yielded openings for Sean O'Connor and Ryan Brennan which Peter Cherrie kept out.
But a period of sloppy Hoops defending culminated in a Dundalk breakthrough before the break.
Rovers complained that Dave McKeon's decision to award a free for a foul on Patrick Hoban was harsh, but they then dozed, with the striker dusting himself down to head the subsequent Darren Meenan delivery past Barry Murphy.
The key period of this game came after the restart as Dundalk sought to put the tie beyond doubt, with Hoban smashing the crossbar and then denied by a fine Murphy save.
Then the Rovers netminder dashed to his back post to push an Andy Boyle attempt to safety.
Fenlon's charges were on the ropes, yet they managed to escape, with the arrival of Stephen McPhail helping them to enjoy better possession in the middle as Dundalk began to drop a little deeper.
Still, they had created little by way of chances when Fenlon played his final hand in the form of Sheppard with 13 minutes remaining.
It worked inside four minutes, with Dundalk crying foul as O'Connor won possession in midfield and split the home defence with a pass that Sheppard calmly converted.
Rovers sensed blood and struck a winner in the 88th minute, with Sheppard again breaching the offside trap, and showing more composure than his pursuers by switching to his left foot and finding a way past Cherrie to prompt scenes of wild celebration.
Dundalk - Cherrie, Gannon, Boyle, Rossiter (Higgins 88), Massey; Shields, Towell; Meenan (McMillan 88), Byrne (Mountney 67), Horgan; Hoban
Shamrock Rovers - Murphy, Madden, Kenna, McGuinness, Byrne; Cregg, Robinson (McPhail 62); Brennan (Waters 54), Finn, O'Connor; Kelly (Sheppard 77)
Ref - D McKeon (Dublin)