St Patrick's Athletic bounced back from their defeat to Shamrock Rovers last week by putting Dundalk to the sword at Oriel Park, with Matty Smith scoring twice as they hit four in the league for the second time this season.
Dundalk were unable to build on their excellent UEFA Conference League result against Vitesse Arnhem in midweek and second place Pats made them pay.
Nahum Melvin-Lambert and Chris Forrester got their other goals in a statement victory.
It keeps them three points shy of leaders Shamrock Rovers, albeit having played a game more.
With Thursday night in Tallaght in mind, Vinny Perth turned to Patrick Hoban in attack, in place of David McMillan.
Cameron Dummigan, Sean Murray and Will Patching also came in.
Stephen O'Donnell made four changes himself, with Robbie Benson missing through injury. Melvin-Lambert, just 18, was handed a first start. His only previous goal for the Saints had been a short hop up the M1, against Drogheda United.
The English teenager, on loan from Reading, must like playing in the Wee County.
Just 12 minutes had elapsed when he found the net again. An almighty goalmouth scramble ensued when the home side failed to clear their lines. John Mountney's shot was parried by Alessio Abibi but Melvin-Lambert was well placed in the six-yard box to finish.
Dundalk had started brightly and had the better of the opening stages before that opener. Michael Duffy and Hoban had glimpses at goal but nothing more.
It didn’t take long for the leveller to arrive though. In keeping with their second goal in Arnhem, it came at the end of a counter attack that caught Pats out. Thursday’s hero Patrick McEleney stole the ball from Alfie Lewis and embarked on a run into acres of space in the opposition half.
He slid in Michael Duffy who unselfishly squared for Patrick Hoban who stretched to apply the finishing touch from yard out.
Three of the previous four meetings between these sides had finished one goal a piece but Matty Smith ensured there would be no repeat of that scoreline shortly before the interval.
Dundalk failed to clear from a corner and after Jason McClelland’s shot was blocked, the ball fell to Smith who drilled past Abibi at his near post.
Despite Shamrock Rovers managing to eek out a victory – leaving it very late to beat basement side Longford - the victory at Oriel Park breathes new life into Pat’s title quest. It is their first win there in nine years.
Genuine chances were at a premium for both teams in the early stages of a second half that was an even tussle for the most part. That was until Abibi was responsible for the concession of a cheap penalty kick.
He barged out of his goal to chase down substitute Billy King after a cross from the left had beaten both in the six yard box. The Italian-born Albanian goalkeeper’s attempt to claim the ball forced King to the ground.
Chris Forrester scored the penalty and then Smith wrapped up the scoring in what was the Scot’s seventh goal of a productive season.
When two goals behind, Sean Murray went closest for Dundalk and should have scored to make it 2-3.
That might have changed things but ifs and buts don’t equal results which has been a theme of Dundalk's league season.
Dundalk: Alessio Abibi; Raivis Jurkovskis (Sonni Nattestad, 75), Cameron Dummigan, Andy Boyle, Darragh Leahy; Greg Sloggett (Sam Stanton, 46), Sean Murray; Patrick McEleney (Han Jeongwoo, 87), Will Patching (David McMillan, 70), Michael Duffy (Wilfried Zahibo, 87); Patrick Hoban.
St Patrick’s Athletic: Viteslav Jaros; John Mountney (Sam Bone, 52), Lee Desmond, Paddy Barrett, Ian Bermingham; Alfie Lewis, Chris Forrester (Jamie Lennon, 79), Ben McCormack, Jason McClelland; Mattie Smith, Nahum Melvin-Lambert (Billy King, 66).
Referee: Rob Harvey (Dublin)