St Pat's took the points from an entertaining encounter at Richmond Park but it came at a price.
Mark Leech, who netted the opener, left the ground on a stretcher while Gary Dempsey was carried off on 87 minutes.
Leech headed the first in on 36 minutes after an Alan Cawley free-kick but went off with a serious looking injury to his right leg on 56.
Kyle Moran made it two on 78 against a Dundalk side that came more into the game in the second period but couldn't break down a resilient Pat's.
On a breezy and cold Dublin evening, the rain began to fall as the game kicked off leaving a greasy surface on the partially re-sodden Inchicore pitch.
Pat's had a chance to take an early advantage on three minutes when awarded a free-kick after Michael Daly took down Mark Quigley just outside the area. Cawley struck the free sweetly but his effort went inches over the bar.
Cawley, Ryan Guy, Dempsey and Quigley were involved in a super move on eight minutes from inside their own half but it ended with Damian Lynch who failed to find a team-mate when he sent the ball in from deep on the right.
Pat's were keeping Dundalk quiet and the Louth side, who started the game with a 3-5-2 formation, freshened things up around the 25-minute mark by switching back to a more familiar 4-4-2. They had shouts for a penalty turned down on 27 when Darren Mansaram went down under a Jason Gavin challenge.
Pat's always looked the more likely to take the lead and that's what they did on 36 minutes when Leech had a powerful free header into Kilmainham end goal after a Cawley free, in a situation where the Dundalk defence should have done better.
They then had their own claim for a penalty on 39 when Quigley went down in a challenge with Chris Bennion but referee Tom Connolly wasn't impressed. Bennion was involved again on 47 when he denied blocked Guy's curling shot.
Pat's were dealt a blow on 56 when Leech went off having gone over on his right leg. He was helped from the pitch and went straight to the dressing room for treatment.
Dundalk had a little more bite about them in the second half with some excellent balls from midfield for Mansaram and Declan O'Brien up front, while the mercurial George O'Callaghan got more stuck in and Daly struck the crossbar on 70.
With 15 minutes left on the clock Leech, who was visited in the
dressing room by his father, the former Irish international Mick, left the ground on a stretcher.
Kyle Moran, who had come on for Leech, made sure of the points when he beat Bennion from close range on 78, but there was more misery for Pat's on 87 when Dempsey was stretched off. The delay led to six minutes of injury-time.