Brendan McGill well-taken winner, coupled to Finn Harps' coming from behind to beat Drogheda at United Park, relegated UCD after four seasons in the Premier Division.
Utterly dominant from the start, champions Bohemians showed little mercy as they deservedly went in front on 20 minutes.
The College defence looked suspect from the fifth minute when Glen Crowe looped a header over the top from McGill's cross.
Glen Cronin flicked a header wide following a scramble while skipper Owen Heary also headed off target from McGill's corner.
UCD's goal was finally breached when Mark Rossiter's sublime ball put McGill in behind and the winger confidently slipped the ball past Matt Gregg.
Gregg had to come to the rescue to prevent a second Bohs goal a minute before the break when tipping over Jason Byrne's well-struck shot from the right.
Lithuanian Mindaugas Kalonas showed some super feet to curl a shot just wide four minutes into the second half as Bohs continued to dominate.
UCD finally troubled Brian Murphy on 56 minutes when Brian King's 35-yarder forced the Bohs keeper to touch the ball round a post.
But normal service resumed at the other end when Bohs should have doubled their lead from an unlikely source on 64 minutes.
Jason Byrne's cross picked out defenders Liam Burns, who'd stayed up for a corner that was only half cleared, at the back post and Gregg had to save well with this feet.
Shane McFaul had UCD's best opening of the night on 78 minutes, but Murphy was equal to it, standing big to make the save from point blank range.
UCD: Gregg; Shortall, McMillan, Kenna, Bermingham; Finn, McFaul, King (Cahalane, 77 mins.), Duggan; Purcell (Meenan, 66 mins.), McWalter.
Bohemians: Murphy; O. Heary, Oman, Burns, Rossiter; McGill, O'Donnell (Deegan, h/t), Cronin (T. Heary, 79 mins.), Kalonas; Crowe (Singh, 53 mins), Byrne.
Referee: Damien Hancock (Dublin).
