Robbie Benson’s ninth- minute strike looked like it had put Stephen Kenny’s side on course for a third final in a row.
However, Brandon Miele gave Rovers a second bite of ending their 30-year wait for the FAI Cup next month by earning his side a replay 14 minutes from the end.
The tone for this game was set before kick-off when a flare from the away support set fire to the surface of Oriel.
It was pretty fiery on the field, too, with Stephen Bradley’s side finishing the game with 10 men as Dave McAllister became the fourth Rovers player to see red against Dundalk in five meetings this season.
The home side started the brighter with Patrick McEleney firing just wide on four minutes after being picked out by Dylan Connolly’s cross.
Five minutes later and last year’s beaten finalists hit the front with a superbly worked team goal. Stephen O’Donnell was at the heart of it with a series of one-touch passes that ended with him squaring across the box for Benson to ghost in to fire home with his left foot.
It could have been 2-0 on 12 minutes but for the intervention of Luke Byrne, who blocked on the line from Connolly.
To their credit, Shamrock Rovers grew into the game gradually and almost levelled three minutes before the break when Brandon Miele’s inswinging free from the right was almost turned into his own net by David McMillan, only for Gary Rogers to brilliantly tip over.
Dundalk also went close on the stroke of half-time with Tomer Chencinski touching Patrick McEleney’s 25 yard effort over the bar.
Rovers had the first clear-cut chance of the second half with the ball falling to Gary Shaw six yards out on 53 minutes, but he couldn’t keep his effort down.
Shaw would then turn provider for another good opening on 64 minutes when he flicked on Miele’s free kick towards Ronan Finn at the back post, but his first-time effort was blocked by O’Donnell.
The equaliser did arrive on 76 minutes. Ronan Finn’s cross from the right picked out Miele at the edge of the area and he fired through the legs of Chris Shields to the bottom left hand corner.
Rovers looked the most likely winners at that stage but pressed the self-destruct button three minutes later when McAllister was sent off for a second bookable offence for a high challenge on Shields.
Dundalk thought they had won it a minute from the end when Benson turned the ball home from close range but referee Neil Doyle ruled it out having adjudged O’Donnell to have climbed on Simon Madden’s back in knocking a header down to his fellow midfielder.
The replay will take place in Tallaght on Tuesday, October 10.
Rogers; Gannon, Gartland, Hoare, Vemmelund; O’Donnell, Benson; Connolly (Shields 71) (McGrath 82), McEleney, Duffy; McMillan (Stewart 91).
Chencinski; Madden, Lopes, Grace, Byrne; Clarke (Webster 94), McAllister, Finn, Bolger (Doona 73), Miele (Connolly 81); Shaw.
N Doyle (Dublin).