This was a night which prolongs two emerging themes of this League of Ireland season.
The first is the continued struggles of St Patrick's Athletic who already look to be out of the title race following a fourth defeat which leaves them 16 points off the pace.
Perhaps they can draw some consolation from the other recurring story, the continued excellence of a Dundalk side that will have everybody else playing for second if they keep up this pace.
Granted, Stephen Kenny's side fell short of their maximum performance bar here, especially after the interval when they were almost too comfortable against ten men.
Yet the fact that they were in a position to be guilty of complacency in what should be one of the toughest fixtures in their title defence emphasises the strength of their current position.
After all, this was a fixture where the Saints had the greater need for three points following a costly slip-up in Bray last weekend.
Alas, they were the architects of their own downfall in a first half where they played with fire against a fit and confident Dundalk team that can be ruthless when teams err in possession.
In a game that began at a lively tempo, the locals started well with Christy Fagan shooting from distance before Aaron Greene called Gary Rogers into action from inside the area.
As the minutes ticked by, however, the champions began to find space in the Saints' half by soaking up toothless pressure and then countering at speed.
A superb Richie Towell dash almost created a goal of the season contender with his cross teed up by Dave McMillan and volleyed first-time by Daryl Horgan with Brendan Clarke saving brilliantly. The subsequent corner ended with a Killian Brennan goalline clearance from a Dane Massey header and McMillan flick.
Sensing vulnerability, Kenny's charges pressed at pace and they got their reward on the half-hour mark when the ponderous Kenny Browne was dispossessed by Mountney, and McMillan stepped in to release Horgan who did the rest with his right foot.
Browne was carded for his late tackle on Mountney in an attempt to cover his error and his rough night at the office descended when ref Neil Doyle produced a second yellow six minutes later for illegally halting a Towell charge.
It was an unusual dismissal in the sense that Doyle played advantage for both cautions, and the natives were fuming as they felt the officials had showed leniency towards Towell in the early minutes when he rode a fine line.
Buckley withdrew Chris Forrester and sent in Jason McGuinness, yet his rearguard was finding it hard enough to contain Dundalk with 11 men and both Massey and Horgan came close to doubling the interval lead.
The men in black were given a wake-up call shortly after the restart when Fagan wasted a one-on-one by firing into the side netting from a clever Conan Byrne through ball.
What the Louthmen needed was an insurance goal to remove the risk of a sucker punch and it came on the hour mark as Horgan converted the third chance to fall his way since the restart. The Galwegian sealed a fine team move involving Massey and Ronan Finn with a crisp drive past Clarke.
That was effectively game over as Saints followers fell silent and Dundalk looked to add a third via elaborate passages of play with McMillan firing inches wide from a prime example.
Much to the frustration of Kenny, the concentration levels dropped as Buckley introduced subs to inject energy in red. Young Jamie McGrath lifted the morale levels with a skilful, weaving run that culminated with a Rogers block from Greene.
The visiting netminder was called into action again to tip a Jason McGuinness header over the bar as the Saints rallied. In the end, it was an unsuccessful damage limitation mission on a sobering night.
St Patrick's Athletic - Clarke, Chambers (Desmond 66), Browne, Hoare, Bermingham; Bolger, Brennan; Byrne, Greene, Forrester; Fagan (McGrath 66)
Dundalk - Rogers, Gannon, Boyle, Barrett, Massey; Shields, Towell; Mountney, Finn (Poynton 90), Horgan (Kelly 88); McMillan (Byrne 81)
ref - N Doyle (Dublin)