Jason McClelland's early winner ended an 11-match losing streak to give depleted UCD’s season a massive lift.
Their first points in 12 games edges the bottom-of-the-table Students to within a point of Harps who have played three games more.
UCD manager Collie O'Neill gave two full debuts as he could name just one outfield player on his bench as the exodus of the side that won promotion last season continues.
Captain Gary O’Neill and winger Neil Farrugia moved to Shamrock Rovers last week with striker Conor Davis leaving over the weekend to sign for Derry City.
Highly rated Republic of Ireland under-21 central defender Liam Scales watched from the stand ahead of his transfer to Bristol Rovers.
To add to O’Neill’s problems, injuries deprived him of Evan Osam, Josh Collins, Jack Ryan, Dara Keane and Sean McDonald.
Despite their woes, UCD stayed true to their principles, passed the ball well, and stunned Harps to take the lead with a well-worked goal after eight minutes for what proved the only strike of the game.
Danu Kinsella-Bishop put McClelland in behind on the left and he advanced before drilling a crisp left foot drive from a tight angle to the far corner of Mark McGinley’s net for a fine finish for his first goal of the season.
Just the confidence boost they needed, UCD continued to trouble Harps, carving the victors open on 20 minutes.
Richie O’Farrell powered through the middle to find Yoyo Mahdy who fired wastefully into the sidenetting.
A mistake by 17-year-old Harry McEvoy, on his first start, should have seen Harps level a minute later.
But Conor Kearns redeemed his young defender’s lapse with a terrific save with his feet from Nathan Boyle.
UCD continued to play and the save of the first half at the other end prevented them from extending their lead on 39 minutes.
Mahdy tenaciously nicked the ball from a sluggish Gareth Harkin before his right-footed drive brought a fine one-handed save at full stretch from McGinley.
But College had a let off from the resulting corner as Harps broke in a swift counterattack.
Caolan McAleer raced away on the right to put Raff Cretaro in on goal. But the veteran’s shot had the sting taken out of it by a deflection off the retreating Evan Farrell as Kearns gathered comfortably.
Boyle then wasted another chance for Harps right on 45 minutes. Having timed his run in behind to perfection onto Jacob Borg’s through ball, the Harps striker shot wide across goal.
Though Harps showed more impetus from the resumption, they struggled to create chances.
The lively McAleer delivered a dipping volley from distance into the arms of Kearns just past the hour.
But Kearns was worked on 70 minutes. Substitute Mark Timlin’s superb cross from the left was met by Daniel O’Reilly whose downward header was brilliantly parried away by Kearns before being scramble clear as UCD held on for a morale-boosting victory.
UCD: Conor Kearns; Dan Tobin, Harry McEvoy, Evan Farrell, Luke Boore; Yoyo Mahdy, Paul Doyle, Jason McClelland, Mark Dignam; Richie O’Farrell; Danu Kinsella Bishop.
Finn Harps: Mark McGinley; Daniel O’Reilly, Keith Cowan, Sam Todd; Jacob Borg (Tony McNamee half-time), Gareth Harkin (Mikey Place 70), Mark Coyle, Mark Russell; Raff Cretaro (Mark Timlin 62); Caolan McAleer, Nathan Boyle.
Referee: Rob Rogers (Dublin)