A brace from Dundalk striker Michael Rafter helped his side to a deserved triumph over a Waterford United side that never turned up for the second leg at a packed RSC.
Sean Maguire should have given the hosts the lead on eight minutes when Paul Phelan whipped in a corner kick that found the head of David Breen and, after the ball fell to the striker, he somehow fired wide from two yards.
Marc Griffin should have put Dundalk in front on 23 minutes when Stephen McDonnell played in a free kick from the left that caused panic in the Blues defence but the attacker blazed over.
As time ticked down at the end of the first half, the Oriel Park outfit struck for the lead goal when Chris Shields hooked a ball in from the right-wing that found Rafter, and the former Waterford player had all the time in the world to turn before finding the net with a left-footed finish.
Referee Padraig Sutton was the centre of attention three minutes into the second half when Maguire went down in the area under a challenge from Liam Burns but the official booked the attacker for diving.
Dundalk 'keeper Peter Cherrie made a fine save on 66 minutes when he kept out a shot from Peter White before making another wonderful stop two minutes later.
Maguire slipped the ball into the path of White, who picked out Ben Ryan but his effort was tipped over the bar.
After the visitors dealt brilliantly with the resulting corner kick, Blues defender John Frost slipped on the halfway line with Rafter taking full advantage to race clear on goal and fire to the corner of the net past the advancing Packie Holden.
Rafter was denied his hat-trick by Blues keeper Holden six minutes from time when his close-range effort was kept out before Mark Griffin drilled the rebound wide of the far post. Maguire then had an effort ruled out for offside before Nathan Murphy struck the post in the final seconds.
WATERFORD UNITED -- Holden; Mernagh, Breen, Long, Frost; Ryan (McGrath 73), White (Coad 75), Dempsey, Phelan (Doherty 56); Maguire, Walshe
DUNDALK -- Cherrie; Gaul, Whelan, Burns (O'Brien 75), Osbourne; Shannon, Shields, McDonnell (Thomas 88), Shanahan (Murphy 60); Griffin, Rafter.
Ref -- P Sutton (Clare)