Goals from Patrick Hoban and Michael Duffy were the difference as Dundalk ran out comfortable winners over a makeshift Shamrock Rovers side.
Hoban became Dundalk's all-time leading goalscorer with his header five minutes from the break, while Duffy's effort came on 60 minutes to secure the three points and cut Rovers' lead at the top of table to four points.
The game started slowly but spurred into life 27 minutes in when Michael Duffy found himself one-on-one with Rovers' keeper Alan Mannus only for his control to let him down.
Not only did this lift the supporters but it seemed to lift the home side who had a flurry of chances following the miss; Hoban denied on two occasions.
It was a baptism by fire for young-debutante James Furlong with Daniel Kelly causing all sorts of problems on the right flank. Dundalk, and Kelly's pressure paid off on 40 minutes as his cross was deflected out for a corner.
Michael Duffy did the honours and his cross was met by the head of Patrick Hoban on the penalty spot and he guided the ball into the far bottom corner.
Shamrock Rovers came out after the break like a team with a point to prove and they could well have been level after just five minutes.
Dan Carr won a free in a good position outside of the box, Jack Byrne provided an excellent ball into the box but Aaron Greene couldn't connect with the ball well enough as it sailed over the bar.
A missed opportunity that they were made regret not soon after as Dundalk doubled their lead through Michael Duffy.
Again Daniel Kelly doing well down the right hand side as he found Sean Gannon on the overlap, he crossed to Duffy at the back post, who calmly fired home to make it 2-0.
Like that, the Lilywhites were in control.
That was until the final ten minutes when Rovers found the net twice in two minutes. The first came from Roberto Lopes with nine minutes to go but his tap-in was deemed offside.
That should have been warning enough for the Dundalk players not to switch off, but just two minutes later the ball was in the back of the net again, this time from Orhan Vojic, this time onside.
A positive display from Dundalk - who have now won four on the trot - in front of the 4,026 in attendance, and it's a result that blows the race for the title wide open.
Just four days ago Shamrock Rovers had a chance to go top by ten, that lead is just four now and the reigning champions are back in the chase.
A more worrying issue for Stephen Bradley will be the growing injury list, as he had to make do with attacking midfielder Ronan Finn having to slot in as a makeshift right back.
Rovers take on St Patrick's Athletic on Monday, while Dundalk travel to Waterford.
Gary Rogers, Sean Gannon, Sean Hoare, Daniel Clearly and Dane Massey, Patrick McEleney (OFF 89 Jarvis), Chris Shields, Jamie McGrath, Michael Duffy,Daniel Kelly (OFF 71 Mountney), Patrick Hoban (OFF 77 Kelly).
Alan Mannus, Roberto Lopes, James Furlong, Joel Coustrain (OFF 62 Kavanagh),Joe O'Brien, Dylan Watts, Aaron McEneff, Jack Byrne, Ronan Finn, Dan Carr (OFF 66 Vojic), Aaron Greene.