Shamrock Rovers were beaten 2-0 at home for the second time this week as Dundalk deservedly took the points at Tallaght Stadium.
In perfect conditions for football, Neal Fenn put the visitors ahead on 35 minutes, slotting in off the post after a Ross Gaynor pass.
Fenn turned provider on 48 minutes with a knock down for Stephen Maher to finish past Rovers keeper Alan Mannus.
The win puts Dundalk third in the table while Rovers have just one point from their opening three games.
After been shocked by St Patrick’s Athletic on Tuesday night, Rovers were looking for a good early start.
Having been in attendance for that game, Dundalk boss Ian Foster looked to stifle Rovers with a 4-3-3 formation, and both sides got stuck in from the off.
Rovers’ Ollie Cahill had a free saved by Dundalk goalkeeper Peter Cherrie after two minute while Dundalk’s Liam Burns met a corner on five minutes but blasted off target.
Cherrie then blocked a shot from Graham Barrett on ten minutes while Rovers’ Billy Dennehy skied his shot on 11.
Cahill took another free on 12 but his effort was tame and Duns cleared easily.
Mannus was alert on 22 to turn the ball around his post after Gaynor’s free took a knock off Aidan Price’s head in the area.
Dennehy then tried his luck again with a shot following a good individual run but fired wide.
Rovers were enjoying most of the play when the Lilywhites went ahead on 35.
Gaynor put Fenn through with a perfectly weighted ball and the former Cork City and Bohemians man slipped the ball past Mannus and into the net off the far post.
Rovers fought back and Cahill crossed a dangerous ball into a packed box on 43 minutes but Dundalk defender Garry Breen hooked the ball to safety.
A goal down, and over-run in midfield, Rovers boss Michael O’Neill opted to make a change for the second 45 minutes, replacing Stephen Rice with Stephen Bradley.
Rovers couldn’t have asked for a worse start to the second period however as former St Pat’s man Maher gratefully accepted Fenn’s knock down after a Burns free on 48 minutes and buried the ball past Mannus.
Rovers pushed on and had plenty of possession and chances but couldn’t find the killer instinct.
One of their closest efforts came on 63 when Pat Sullivan met Sean O’Connor’s corner but sent his header wide.
Duns fans were calling for a penalty on 65 when Mannus and Gaynor collided as they both chased down a ball on the edge of the area but referee didn’t see anything in it.
Creative play from Rovers on 73 minutes saw Cahill tee up O’Connor deep on the left but O’Connor wasted the chance and lost possession.
A minute later Bradley sent a free too high as Rovers strived to get back into the game.
Rovers sub Don Cowan did well to shake off Breen on 80 minutes and get a shot in, but Cherrie was well placed to save.
Rovers tried everything as the game wound down but couldn’t get catch a break.
Shamrock Rovers: Mannus; Sullivan, Price, Murray, Stevens; Rice (Bradley h/t), Bayly, Cahill, Kavanagh (O’Connor 52); Dennehy, Barrett (Cowan 59). Unused subs: Duggan, Sives.
Dundalk: Cherrie; Kelly, Hatswell, Miller, Breen; Miller, Melligan (McGuigan 90+2), Maher; Fenn (Synnott 82), Gaynor (Murphy 87), Kudozovic, Unused subs: Breen, Gregg.
Referee: P Tuite.
Airtricity Man of the Match: Neale Fenn.