Replacements: Jack O'Connell, Steve Collins, Brian Moylett, Tom Kiersey, Gearoid McDonald.
Replacements: Liam Hyland, Adam Clarkin, Michael Cawley, Jamie Glynn, Niall Earls.
Newcomer Scott Deasy started at out-half in life post-Craig Ronaldson for Lansdowne and opted to go down the line from 40 yards five minutes in.
UCD won the lineout and when Ross McCarron gathered the clearance and took the ball into the tackle, UCD quickly turned the ball over. Luke McGrath spread the ball wide and a nice flowing move ended with Conor Gilsenan crossing the whitewash.
Eoin Joyce was sin-binned after 12 minutes for UCD as Lansdowne gained the upper hand up front. Deasy struck two penalties in quick succession on 18 and 20 minutes after further UCD infringements in the ruck. Lansdowne led 6-5.
Lansdowne had a glorious opportunity on 27 minutes when Charlie Butterworth knocked on five metres from the line after they spread the ball wide. Deasy had a chance to make it a four-point game two minutes later but his effort went agonisingly wide.
UCD went into the lead when out-half Thornton nailed a kick from 45 metres to make it 8-6 before Boyle became the second student in the sin-bin with minutes left in the half. Up stepped Deasy to convert and the home side led by a point.
In injury-time a moment of madness from back rower Mark McGroarty brought the students down to 13 men when his boot grazed the head of one of the Lansdowne forwards. In a crucial moment in the game, a crooked put-in halted the headquarters side who led 9-8 at the break.
Lansdowne started the second- alf well and after a Mark Roche break brought them to within inches of the UCD line, flanker Clive Ross knocked on.
While Lansdowne forced the UCD scrum back over their line, they failed to make the scrum count. A loose pass following the scrum saw UCD's Stephen Murphy flick the ball back under his legs to Thornton who set James Tracy and Alex Kelly away.
Tracy failed to hold onto Kelly's return pass and Lansdowne survived. With 10 minutes gone in the second half Thornton restored the students' lead, 11-8.
Another Thornton penalty followed on 57 minutes before Ross was sin-binned for Lansdowne and once again Thornton stepped up to put UCD 17-9 clear.
A scintillating break by scrum half Luke McGrath got the UCD backs going again and winger Daly made it over in the corner when they recycled the ball wide out. Thornton was off target with the conversion but UCD led 22-9.
With 15 minutes remaining Thornton's clearance kick found touch inside the UCD 22 and after winning the the Lansdowne lineout, Murphy's drop goal attempt hit one of the uprights.
Lansdowne reacted quickest and touched the ball down for a UCD scrum five metres out. But UCD got their reward and Boyle touched down after the 'College pack had forced another scrum turnover. Thornton's conversion was wide, but UCD were in dreamland.
There was still time for Cian Aherne to run in a try for Lansdowne while Deasy's conversion went narrowly wide of the far left post.
Lansdowne head coach Mike Ruddock will know that his team need some time to get to know the various new partnerships, in the front row and at half-back in particular.
Meanwhile, his UCD counterpart Byrne will be hoping his first game in the top flight is a sign of things to come for UCD. Their back-line were electric at times and in McGrath and Thornton they have one of the best half-back partnerships in the league.
Referee: Nigel Correll (IRFU)