Mark Quigley showed his class at Richmond Park as St Patrick's Athletic set up a semi-final date with Sligo Rovers.
Back in Inchicore for his second spell with the club, the classy striker bagged a brace and played a part in Conan Byrne's double before Daryl Kavanagh finished off the rout.
Playing their 27th game of this cross-border competition, the Saints had a slender one-goal lead from the first leg to build on and they set about doing just that early on.
As they pushed their Danske Bank Premiership opponents onto the back foot, the hosts found ample room to roam and Quigley sensed a weakness in visiting 'keeper Alvin Rouse.
On 12 minutes, the former Shamrock Rovers man got his goal when he drilled a low free-kick from 25 yards out under the Ballinamallard wall and past the helpless Rouse.
Byrne then got in on the act when converting a rebound from Ian Bermingham's shot before adding his second of the night when Quigley scooped a pass into his path to finish.
A place in the last four was then sealed when Quigley tapped home following a cut-back from substitute Chris Forrester.
Kavanagh added a fifth with a fine strike to put the icing on the cake.
St Patrick's Athletic – Gilmartin; O'Brien, Foran, Oman, Bermingham; McCormack (Forrester 50), Chambers; Byrne (Chindea 79), Lynch (Bolger 53), Kavanagh; Quigley.
Ballinamallard United – Rouse; Beacom, Stafford, Hill, McCartney; Campbell, Kee, Hutchinson (McManus h-t), Currie, Martin (Crawford 66); Lecky (Crilly 79).
Referee – R Rogers (Dublin).