St Patrick's scored more than once for the first time in four months to greatly ease their own relegation fears and plunge Shamrock Rovers into real danger at second from bottom of the table.
The biggest crowd of the season at Richmond Park were all witnesses to a frantic match which, despite the endeavour of all, struggled to produce many scoring chances in the first half.
As just six goals from their previous 16 games attested, St Patrick's problem this season has been in finding the net and they failed to get a shot on target until they stole the lead in first-half stoppage time.
Prior to that, Shamrock Rovers - working equally as hard - looked far more dangerous in front of goal; Lee Roche signalling their intent when his close-range shot was deflected for their first corner of the night on 16 minutes.
And, back in the side from the start, Marc Kenny's accurate deliveries from set-pieces were forcing St Patrick's to defend diligently.
When they didn't, as from a Trevor Molloy header from Kenny's free-kick on 22 minutes, Barry Ryan was there to make the save.
An even better stop was required from Ryan 11 minutes later. Kieran Foley, moved up front from central defence as Rovers went with three at the back, helped on Mark Rutherford's pass to Molloy, whose powerful drive was held by the St Patrick's captain.
And Rutherford had to make a terrific saving tackle to take the ball off the toe of Stephen Brennan on 42 minutes before St Patrick's stole the lead.
Keith Doyle's foul on namesake Robbie was duly punished by St Patrick's Athletic dead-ball specialist Alan Reilly who walloped his free-kick straight through the poorly-arranged wall.
St Patrick's lost Ryan to injury early in the second half, but defended stoutly everything Rovers could throw at them to break away for their killer second goal on 69 minutes.
Reilly's sublime through ball found the run of Gerard Rowe, who raced through to slide the ball past Barry Murphy and in off a post.
Rutherford gave Shamrock Rovers hope when side-footing home on 88 minutes.
But St Patrick's Athletic had the final say when Shamrock Rovers defender Gavin McDonnell kicked out at Seán O'Connor after fouling him inside the area and referee Alan Kelly - who hadn't given the penalty for the initial challenge - pointed to the spot.
McDonnell was sent off and Doyle stepped up to send Murphy the wrong way.
ST PATRICK'S ATHLETIC: Ryan (Clarke, 58 mins); Quigley, Caffrey, Maguire, Frost; Brennan, Donnelly, Reilly (O'Connor, 86 mins), Doyle; Rowe, Larsen (Maher, half-time).
SHAMROCK ROVERS: Murphy; Shelley, McDonnell, Foley, Doyle; Tracey, McDonagh, Kenny (Manley, 70 mins), Rutherford; Molloy, Roche (O'Connor, 53 mins).
Referee: A Kelly (Cork).
