First half goals from Brian Shortall and David McMillan gave the Saints a 2-0 half time lead and Crumlin let Pats dominate in the second half- with Daniel Loughran sent off and Jake Carroll cementing the win for Pats with a fantastic goal.
After a start which saw their unfancied visitors have a lot of time on the ball, Pats took the lead after 16 minutes with a header from what was their fourth corner of the match. The unmarked Brian Shortall stooped low to head in Jordan Keegan's delivery past Dave Meehan.
To their credit, Crumlin, who have won three of the last four FAI Intermediate Cups, never really looked out of their depth. The difference between the sides in the first half seemed to be that Pats had more of a cutting edge about them. Ian Daly put in a good shift in attack, threatening the Crumlin goal again on 26 minutes with a long-range shot which fell just over.
An Anto Murphy cross on 33 minutes fell wonderfully for David McMillan right in front of goal, and McMillan just about got in front of his marker to volley the ball in powerfully. Pats attempted to snuff out the Crumlin challenge by holding the ball, but United weren't content to hold possession when they had it - making for an entertaining end to the first half.
The Saints were able to truly get control of the game after the half-time break. Crumlin started brightly, but before long Pats were able to pass the ball around at their own leisure. The visitors went closest after 55 minutes, with a dangerous-looking cross no-one could get on the end of, but never looked like making a comeback.
Daniel Loughran - nephew of Crumlin manager Martin - didn't help his side by getting sent off after 59 minutes for a harsh tackle on Sean Stewart. Pats used their numerical advantage to completely control the match from then on, scoring a third goal seven minutes after the sending off. Jake Carroll capped a fine performance by scoring from a free-kick on the edge of the Crumlin box- looping his shot over the wall and into the top-left corner of the Crumlin goal.
Pats could have won by more. In the box and in space, Sean Stewart shot just wide after 77 minutes after a sublime pass to him by David McMillan. Ian Daly shot wide from inside the Crumlin box on 85 minutes, but in the end 3-0 was the result and Pats take on more step towards that holy grail of the FAI Cup.
Crumlin United: Dave Meehan, Derek Griffin, Carl Redmond, Paul McCabe, Peter Sherlock, Ciaran Reilly, Stephen Larkin, Andy Doolin, Tony Griffiths, Daniel Loughran, Alan McGreal (Robert Douglas, '67)
Subs not used: Damien Cuffe, Niall Cooney, Stephen Gough, John O'Connor, Daniel Woods, Simon Lowery.
St Patrick's Athletic: Chris Bennion, Derek Pender (Sean Stewart '47), Jake Carroll, Brian Shortall (Paul Crowley '64), Evan McMillan (Ian Bermingham 78), Anto Murphy, Shane McFaul, David Mulcahy, David McMillan, Ian Daly, Jordan Keegan
Subs not used: Gary Rogers, Stephen Bradley, Daryl Kavanagh, Danny North.
Referee: Neil Doyle
Attendance: 700 (estimate)
Extratime.ie Man of the Match: Jake Carroll