Captain Stephen O'Donnell, David McMillan, Daryl Horgan and Brian Gartland were among the goals as champions Dundalk responded in clinical fashion to last Friday's home defeat to Cork City to go back top of the Premier Division table.
Three straight wins saw an in-form St Patrick's, unchanged for the third consecutive game, start confidently at Richmond Park.
But it was a false dawn for the home faithful in the crowd of 2,150 as a defensive blunder gifted the Dundalk the lead on nine minutes. All the more ironic given St Pat's boss Liam Buckley had praised his defence ahead of the game for their having kept three successive clean sheets.
An attempted pass by Shane McEleney to Keith Treacy fell way short. Alert to the opening, O'Donnell nipped in to run on and shoot past Brendan Clarke.
Reeling from that after their bright start, St Pat's were close to finding themselves further behind two minutes later. Ciaran Kilduff's overhead kick from Chris Shields' lobbed cross was deflected for a corner.
John Mountney then cut in from the right flank to shoot narrowly wide as the home side struggled to regain its early composure.
They did regain it, however, to carve three openings in quick succession either side of the 20 minute mark.
A powerful effort from distance by Treacy wasn't far wide before Dundalk keeper Gary Rogers was worked in getting his fingertips to Christy Fagan's shot on the turn. Fagan was then off target with a left foot drive from the edge of the area in a vibrant game.
Dundalk always remained the more menacing when they got forward, though. Horgan's quick feet making room for the winger to drill a shot wide on 33 minutes.
Seven minutes later Kilduff should have done better than shoot tamely at Clarke after Sean Gannon availed of a Billy Dennehy error to set him up.
The big striker did do better a minute before the interval, his downward header from Mountney's corner eventually gathered on the line by Clarke.
A surprise change for St Pat's at the interval saw Fagan withdrawn as Dinny Corcoran came in up top.
And though they began the second half with some impetus with efforts from Darren Dennehy and Timlin coming close, Dundalk wrapped up the points with two goals in six minutes midway through the half.
On the pitch just over a minute, McMillan collected Horgan's pass just inside the box to turn and leave Clarke rooted to the spot with a right foot shot on 64 minutes.
Horgan capped a fine display with the third goal six minutes later, his shot from the edge of the area finding the bottom corner of the net.
Left negligently marked, central defender Gartland met Robbie Benson's free kick to add the fourth goal in the first minute of stoppage time.