Georgie Kelly scored twice to mercilessly down his home county team with his first goals for St Patrick's Athletic.
Donegal native Kelly, on loan from champions Dundalk, struck twice midway through a first half the home side dominated.
The much-improved performance and result was just what St Pat's coach Stephen O'Donnell ordered after last Monday's home defeat to Derry. It edges St Pat's up to fourth in the Premier Division overnight as Harps slumped to a fifth successive defeat.
With Robbie Benson playing in an advanced role behind Kelly, St Pat's started on the front foot, enjoying all the early possession.
But it was Harps who carved the first half chance of the game following an 11th minute corner - Tony McNamee's deflected shot comfortably gathered by Brendan Clarke.
It mattered not, though, as St Pat's took the lead with a delightfully worked goal on 14 minutes.
David Titov raided down the right to feed Benson. Benson used his strength to turn his marker before slipping former Dundalk team-mate Kelly in with a sublime pass to drill a shot beyond Mark McGinley.
Harps survived falling further behind three minutes later when defender Luke McNally's audacious back flick from Jason McClelland's corner was inches over the crossbar.
A dreadful defensive blunder then gifted the home side a second goal on 27 minutes. There was no pressure on Kosovar Sadiki from McClelland's header forward. But the Canadian central defender's attempted back pass was under-hit allowing Kelly in to take the ball around McGinley and tap home his second goal.
Having turned a Rory Feely's header round post moments earlier, McGinley deprived Kelly of his hat-trick on 62 minutes when saving well with his body. The sides meet again at Finn Park on Monday night in the first round of the FAI Cup.
St Patrick's Athletic - Clarke; Feely, McNally, Bermingham; Titov, Forrester, Lennon (Ward, 69), McClelland (Markey, 80), Griffin; Benson (Desmond, 69); Kelly (Gibson, 80).
Finn Harps - McGinley; Webster (Doherty, 85), Sadiki, Folan, Todd; Coyle (Delap, 69), McEleney (R Harkin, 69), Connolly, T McNamee; O'Sullivan (Russell, 85); Kogler (Cretaro, ht).
Ref - S Grant (Wexford) (* replaced by fourth official Paul McLaughlin (Monaghan) after 75 minutes)