This all came down to one last drive for glory.
Blackrock’s lineout at the end of hooker Sean Molony’s throw and jet-propelled maul put them into position.
When all other options had been taken, it was their backs who made light of the heightened pressure to deliver under stress as the clock turned red.
Captain Liam Turner was the key to drawing in defenders, the centre slicing an angle before the release came for right wing Adam Thompson to make the whitewash in one final thrust.
The conversion from out-half Joey Caputo – son of Leinster scrum coach Marco – was caressed through the posts as referee Dermot Blake signalled the end of a thrilling contest.
The Belvedere crew had no cause for regret. They had given their all. It looked as though it would be enough for so long.
Although the Williamstown school began fluently to carve out a sixth minute penalty for Caputo, they were driven onto the back foot.
Belvedere were building on carrying from lock Luke McDermott, prop James Gleeson and No 8 Ruadhan Byron against a defence led by back-rows Michael McGagh and Liam McMahon.
Blackrock captain Liam Turner’s burst from deep and a splintering maul put 'Rock back where they wanted to be. They just couldn’t hold onto the ball.
A towering garryowen from Belvo out-half David Hawkshaw had scrum-half Louis O’Reilly scrambling to do well to reclaim the ball.
However, the forwards came as a package and the turnover allowed Belvedere scrum-half Ted Walsh to kick ahead for wing Sam Barry to dot down to make it 5-3 in the 27th minute.
It stayed that way to the break and beyond as defences were just about able to hold out.
Eventually, Turner’s counter was stopped by centre David Sanfey’s alert take-down.
The pressure told when referee Dermot Blake noticed an indiscretion for Caputo to make it 6-5 in the 50th minute.
This meant the responsibility lay with Belvedere to react and they did so with impressive ball retention to earn a penalty, posted by full-back David Lacey in the 56th minute.
It all came down to the last play, Thompson putting Blackrock into the final where they will meet the winners of tomorrow’s semi-final between Terenure and Roscrea.
Blackrock – N Brady; A Thompson, L Turner (capt), R Hally-Doody, D Colgan; J Caputo, L O’Reilly (H Donnelly 55); G Coyne, S Molony, T Clarkson (R Gallagher 58), T Godson-Treacy (M Grogan 55), J Stapleton, J Burke (J Slevin 55), M McGagh, L McMahon.
Belvedere – D Lacey; J Crumlish, D Sanfey (J Meagher 56), C Mulvaney, S Barry; D Hawkshaw, T Walsh; J Gleeson, L McGrath (J Haughey 53), J Bell (M Hynes 48), L McDermott, M Daly, J McComish, H Beggy (capt), R Byron.
Ref – D Blake (Leinster Branch).