Limerick showed no adverse affects to their managerial upheaval during the week as interim boss Willie Boland's side came away from Richmond Park with a big three points.
Brendan Clarke saved a penalty as he returned to torment his beloved St Pat's either side of goals from Tony Whitehead and John O'Flynn winning it for the Shannonsiders.
St Pat's saw more of the ball in a relatively quiet opening; Josh O'Hanlon heading tamely over the top from Kurtis Byrne's cross in from the left on eight minutes.
But it was Limerick who had the first clearcut chance two minutes later. Rodrigo Tosi showed clever feet to get tuned on the edge of the area before his low drive brought a decent diving save from Conor O'Malley.
In an open game, in which both sides passed the ball well, the St Pat's keeper was worked again on 17 minutes, getting down to his left to save from Shane Duggan's shot from outside the area after Chris Mulhall picked out his skipper with a ball in from the right flank.
Lee-J Lynch and then Duggan, in turn, blazed effort over the home crossbar as Limerick got on top.
The home goal was now leading a charmed lift as O'Malley was called on to make this third save of the game on 24 minutes after Tosi played Chiedozie Ogbene through on the left to shoot.
A goal was coming for Limerick and they deservedly got it two minutes later.
Duggan whipped in a low free kick from the left with central defender Whitehead wheeling away claiming to have got the final touch to flick the ball past O'Malley.
Limerick maintained their positive start as the overworked O'Malley was called on once again to rescue St Pat's with yet another save from Tosi's clever volley after Ogbene got to the end line to cross.
St Pat's finally came alive just before half-time; Lee Desmond bringing a save at the back post from Clarke from a JJ Lunney corner.
Kurtis Byrne then saw his lobbed cross come back off the top of the Limerick crossbar.
There was far more impetus to St Pat's play on the resumption with Conan Byrne heading wide from skipper Ian Bemingham's deep cross minutes in.
Kurtis Byrne then brought a terrific one-handed save from Clarke with a curling shot after Alex O'Hanlon threaded a ball through to him.
Limerick then had a miraculous let off on 64 minutes after conceding a penalty for a handball.
Conan Byrne stepped up, but former team-mate Clarke dived the right way to save. Birmingham then saw his follow-up shot come back off a post.
Duggan relieved the pressure on Limerick on 78 minutes when worming his way into the home area to bring a save from O'Malley at the foot of a post.
And O'Malley was in the way again to deprive substitute O'Flynn with a smother save.
But O'Flynn wasn't to be denied as he sealed Limerick's win with their second goal on the counterattack on 83 minutes.Â
Clarke's clearance found Ogbene who put O'Flynn through to slide past O'Malley.