Lansdowne took the lead after just two minutes when UCC were quickly stripped of possession and winger Charles O'Callaghan had the pace to dart a full 70 metres to the try-line, with out-half Will McEvoy's conversion attempt just drifting wide.
And while UCC responded via an Andrew Burke penalty, 'College were rocked within minutes when Lansdowne ran the length of the field from a UCC intercept pass to score through Niall Cullen in the corner to lead 10-3.
As the half progressed, 'College were visibly getting to grips with their opponents and were rewarded with another Burke penalty on the stroke of half-time.
There was a turning point very early in the second half when team captian Gavin Nugent stopped a certain seven-pointer by intercepting a pass.
UCC's pack were now dominant and were rewarded with Burke's third penalty of the day to leave it 10-9 to the Dublin side with 50 minutes on the clock.
'College continued to press in the Lansdowne half and got the all important break through in the 62nd minute when Burke went under the posts, following great driving from the pack.
The score made it 16-10 to UCC, with Lansdowne number 8 Conor O'Donnell in the sin-bin.
No one present would have thought that there would have been no further scores in this exciting game.
UCC were aware that there was going to be a substantial amount of injury-time following two injuries to outstanding number 8 James Ryan - the second which saw him substituted - but the nine minutes that followed were far more than UCC had hoped for.
They defended in that period deep in their own 22 as if their lives depended on it, and while Lansdowne, with Shane Gahan, Dominic Ryan and Ferdia Doherty to the fore, came close to spoiling the party on a number of occasions, defeat was never going to be UCC's lot on the day.
A fifth All-Ireland Under-21 title for UCC in this competition's 15-year history marks a unique achievement.
Some other players who have won an All Ireland U-21 title with UCC include Ronan O'Gara, Peter Stringer, Jerry Flannery, Denis Leamy, Donnacha Ryan, Denis Hurley, Stephen Keogh, Frank Murphy and Timmy Ryan.
UCC: Andrew Burke; Gavin Nugent (capt), Joe Holland, Patrick Paffrey, Olan Dennehy; Johnny Holland, Daryl Foley; Gavin Duffy, Andrew Cudmore, Shane Moynihan, Brian Quill, David O'Callaghan, Brian O'Callaghan, Johnny MacCarthy, James Ryan.
Replacements: Damien Cahalan, Bryan Cagney, Rory O'Donovan, Conail Murphy, Joe Coyne, Andy O'Leary, Kevin Kidney.
Management Team: Richard Kelleher (Head Coach), Rory Mc Grath (Forwards) Johnny Kenefick (Backs), Leo Murphy (Scrum), John Bradfield (Manager), Brian O'Connor (Assistant), Dave Angland (Physio), Colin Murphy & Jeff Gomez (Strength & Conditioning), Len Browne & Nollaig Parfrey (Analysis), Gary Byrne (Director of Rugby).