Finn Harps defeated UCD 3-1 on aggregate to set up a promotion-relegation playoff with Limerick.
After a 1-0 win at the College Bowl, Ollie Horgan's side saw their aggregate advantage cancelled out by Jamie Doyle, but late goals from Nathan Boyle and Josh Mailey saw Harps advance to play Limerick.
Over 2,000 fans were in attendance at Finn Park, but saw the hosts fall behind when Robbie Benson crossed for Doyle to head home. However, Horgan's men restored their advantage with a low strike from Boyle.
UCD pushed men forward to find a second, but this left them exposed at the back, allowing Mailey to beat Conor O'Donnell from the edge of the area with a well-taken strike.
Finn Harps will travel to Market's Field on Monday, November 2 before hosting Limerick in Ballybofey on Friday, November 6.