Dundalk recorded their first win over Cork City since October 2016 thanks to Patrick Hoban's early goal at Oriel Park on Friday night.
The result cuts the gap between the bitter rivals to just a solitary point. John Caulfield's side still lead the way after beginning the season with three straight wins but Stephen Kenny's side look like they are really motoring now with nine goals scored and none conceded from their four matches to date.
This fixture has become the highlight of the SSE Airtricity League calendar and things began at a blistering speed with Dundalk exploding from the blocks and scoring the only goal of the game after four minutes.
Mark McNulty, who has been something of a pantomime villain for Dundalk supporters over the past couple of years, suddenly became the toast of Oriel Park by inexplicably letting Ronan Murray's free-kick squirm from his grasp and Hoban was there to accept the gift.
Jamie McGrath drives at the Cork defence in the second half as he's chased by Gearoid Morrissey
The champions looked rattled and Caulfield moved quickly to stop captain Conor McCormack from picking up a red card by withdrawing him with just 20 minutes played.
At that stage, Dundalk were looking for a second with McNulty making an excellent save to divert a deflected Dane Massey effort around his post. The back peddling Shane Griffin then scooped Murray's goal bound drive over his own bar.
Cork eventually cleared their heads and Barry McNamee, McCormack's replacement, almost restored parity against the run of play in the 33rd minute but Gary Rogers advanced to narrow the angle and Dan Cleary showed good positioning to clear Kieran Sadlier's follow-up over the top.
The hosts started the second half in similar fashion and Hoban dragged a right-footer agonisingly wide with Cork all over the place at the back.
Alan Bennett's absence in the Cork back four was highlighted again in the 63rd minute when Aaron Barry dropped a clearance straight into the path of Jamie McGrath but the Meathman couldn't punish Cork, shooting straight at McNulty.
The champions continued to teeter on the brink and it looked like Kenny's side would eventually put it to bed when Benson was upended in the box by Barry but McNulty - like he did to win last November's FAI Cup final - made a fine stop to turn the spot kick around the post.
With Kieran Sadlier and Graham Cummins struggling to make an impression, Cork never raised a gallop and Dundalk saw it out relatively comfortably to send out a big statement of intent.
Dundalk FC: Gary Rogers; Sean Gannon, Sean Hoare, Dan Cleary, Dane Massey; Chris Shields, Robbie Benson; Jamie McGrath (Dean Jarvis 90); Ronan Murray (Karolis Chvedukas 78), Michael Duffy, Patrick Hoban (Marco Tagbajumi 89).
Cork City: Mark McNulty; Steven Beattie, Aaron Barry, Conor McCarthy, Shane Griffin; Conor McCormack (Barry McNamee 21), Gearoid Morrissey; Karl Sheppard, Garry Buckley (Jimmy Keohane 77), Kieran Sadlier; Graham Cummins.
Referee: Paul McLaughlin.