UCD held off a brave second half surge from Dublin University before securing the spoils, 32-19, in an Ulster Bank League encounter that doubled up as the 65th annual Colours match.
Leinster duo Andrew Porter and Barry Daly both touched down for the victors at sunny Belfield, with lively winger Tommy O'Brien bagging a brace and fellow Ireland Under-20 international Ciaran Frawley kicking 12 points.
Bryan Mollen, who starred for the Ireland Students team against England last Sunday, converted his own try as Trinity trailed 17-7 at half-time, and although their scrum forced a penalty try and Ireland Under-19 call-up Michael Silvester also touched down, Tony Smeeth's youngsters relinquished their grip on the Colours trophy.
As well as Division 1A points, bragging rights were also at stake in this meeting of the long-standing University rivals. Trinity secured a 28-15 victory at College Park in last year's Colours fixture, and nine of their matchday squad returned from that memorable outing. UCD had nine players making their Colours debuts.
Mollen, one of seven ex-Blackrock College students in the Trinity starting line-up, drifted a 30-metre penalty past the left hand post in the fifth minute, and from their very first attack, UCD duly opened the scoring as prop Porter, who is getting game-time at tighthead lately, powered over the line at the end of a multi-phase move.
Full-back Frawley converted from close range and he then tagged on a penalty for a 10-0 lead in the second quarter, rewarding some good work from the UCD pack who had a man-of-the-match performance from number 8 Peadar Timmins.
Trinity hit back in the 29th minute when good work from captain Brian Slater got them into scoring range and Colm Hogan's audacious pass put Mollen over for a try in the left which he converted with aplomb.
UCD responded in the final minute of the half, though, as O'Brien grounded the ball over the whitewash after racing onto his own kick towards the Trinity line. Frawley added the extras to restore the 10-point gap – 17-7.
The visitors suffered another setback 12 minutes into the second period, Daly getting over for a breakaway try after out-half Matthew Gilsenan had done brilliantly to swoop on a loose ball and release the big winger with a diving pass. Mollen almost broke free at the end of the third quarter but UCD scrambled back to deny him.
With Andy 'Panda' Keating to the fore, Trinity put the pressure on at a series of scrums and referee Kieran Barry rewarded them with a penalty try which Mollen converted to cut the gap to eight points (22-14), and a losing bonus point – at the least – was there to aim for.
Smeeth's charges look re-energised and despite missing out on a try when number 8 Tom Ryan went close, teenage replacement Silvester exploited some space in behind the UCD cover to notch an unconverted try, making it a three-point game.
After Mollen's missed conversion, UCD got on the front foot again and spread the ball effectively. With six minutes remaining, a slick offload from Gavin Mullin, whose father Brendan is part of Trinity's great Colours history, put O'Brien through for UCD's clinching try which Frawley converted.
The Skerries man, who was one of Ireland's leading backs during the recent U-20 Six Nations, completed his kicking haul with an 80th minute penalty as UCD secured their 39th Colours title. Trinity have 22 wins and four matches have been drawn.
Referee: Kieran Barry (IRFU)