John Mountney's first goal for Dundalk was enough to see the Louth club advance to the next round of the FAI Cup at the expense of St Patrick's CY.
Mountney struck in the 49th minute, sending a low effort through a crowd of bodies to give the nine-time FAI Cup winners a narrow victory.
Dundalk missed an 80th minute penalty from Michael Rafter to kill the tie and they almost paid for their wastefulness when Gary O'Connor went close with a free-kick for St Pat's just two minutes later.
Lilywhites boss Sean McCaffrey was able to name Mark Griffin, hit two goals for Dundalk in their victory over St Patrick's Athletic just four days previously, in his starting line up for the first time this season.
St Patrick's CY arrived having already taken the scalp of an Airtricity League Premier Division outfit when they beat Bray Wanderers 3-0 in the Leinster Senior Cup.
The hosts bossed the early exchanges and Griffin squandered two glorious chances to open the scoring.
He shot against Pat's goalkeeper Philip O'Connor after being slipped through by Michael Rafter inside the first minute and shortly after he somehow turned the ball over the bar from inside the six-yard box when he looked certain to score.
The Leinster Senior League side settled to the task at hand and manager John Young will have been happy with his team's first-half showing. Playing five men across the middle, the Ringsend-based side frustrated Dundalk with their disciplined approach.
The home side did have a sighting of goal in the 20th minute but Stephen McDonnell blazed over and the sides went in scoreless at the break.
Dundalk started the second-half like they started the first and Rafter saw his blockbuster brilliantly saved by O'Connor in the 48th minute.
There was relief for the nine-time FAI Cup winners just 60 seconds later. O'Connor came for a corner that he was never going to get and the fell to Mountney who fired it home through a crowd of bodies for his first Dundalk goal.
The Louth side set about putting the game to bed but they were given a reminder of how slender their lead was in the 64th minute when Alan Murphy saw a long range effort dip on to the crossbar.
Rafter should have put the result beyond doubt but he blazed over from the spot after he was pushed by Simon Dunne.
The visitors almost forced a replay only for Gary O'Connor to see a free fly just over and they ended the game with ten men when Dunne saw red in the final minute.
Dundalk: Peter Cherrie; Ben McLaughlin, Derek Foran, Liam Burns (Robert Waters HT), Eoghan Osborne; Paul Walsh, Chris Shields, John Mountney, Stephen McDonnell (Nathan Murphy 87); Michael Rafter, Marc Griffin (Shane O'Neill 70).
St Patrick's CY: Phillip O'Connor; David Andrews, Thomas Nolan, Simon Dunne, Glen O'Connor; Alan Murphy (Conor Riddick 65), Carl O'Brien, Dean Young, Andy Doolin (Thomas Dunne 65), Gary O'Connor; Lee Roche.
Referee: Tom Connolly (Dublin).