The Saints' young guns convincingly booked themselves a place in the Final of the Enda McGuill Cup tonight in a rainsoaked Gainstown.
A healthy away support survived the dreadful weather conditions while the players took advantage of the excellent pitch with some slick play.
Luke Fitzpatrick had the ball in the net after only 9 minutes but his header was harshly rules out by the referee.
The Saints didn't have to wait long to make the breakthrough however when Darren Sargeant buried a Christy Doran corner past Wallace in the Mullingar nets.
Robbie Smith made it two, 11 minutes before the break. Smith beat the offside trap and latched onto a Peter Darcy pass before sliding the ball into the far corner.
The second half was dominated by the Saints with the aid of a strong breaze while the rain continued to pour.
Joey Hayden got the third on 57 minutes with a delightful lob. Christy Doran (65 mins) and the impressive Luke Fitzpatrick (73 mins)completed the scoring.
With Paul Osam's team scoring freely and Brendan Clarke securing his eighth clean sheat in a row they will be looking forward to Saturday's top of the table clash with UCD.
The Enda McGuill Cup Final will take place on Tuesday, October 4th in the Carlisle grounds, with Bray the opposition having defeated Sligo Rovers 4-2 in the other semi-final.
St Pats Ath: Clarke; Quigley(McMahon), Sargeant, O'Shea, Bell; Fitzpatrick, Hayden (McKeown), Darcy(Doyle G.), Doran(Rooney); Smith(Olima), Rowe.
Mullingar Ath. Wallace; Masterson, McGovern, Ahern, Fagan; Fadian, Thornton, Kelly, Quinn; Lynam, Keegan.