Midfield partners the Colvin brothers, Cillian and Tiernan, used their speed and guile to great effect and punished their opponents with every opportunity.
The second half saw Leinster move ahead with two more goals from Keleghan and one from Cillian Colvin on their way to a 6-0 win.
A focused Ulster team beat a tired Connacht in the second game of the day, 8-3, to set up a titanic final battle with Leinster.
And a battle royale ensued. Leinster drew first blood when Darragh Murphy stepped up and dispatched a penalty.
Ulster had many attacks against Leinster but found a miserly defence in front of them.
Magnificent displays by Dave O'Donnell, Jack Reilly, Bridgeman and Ciaran McCarthy ensured their team held a 2-0 lead at half-time.
The second period saw Ulster up the tempo of the game and some desperate defending saw two sin-bin offences on the Leinster side, but still their defence held firm. Goalkeeper Dave O'Donnell was a tower of strength, as were the Leinster point men, who worked their socks off when they were at a numerical disadvantage.
It turned into a war of attrition but those first-half goals proved decisive as Leinster clung on for a 2-0 victory to spark rapturous celebration from their strong support.
Coach Sean Kenna was thrilled and full of praise for his charges.
"They showed us in both matches that they can make scores and defend depending on who they play," he said.
"Ulster got them at the wrong time and came off second best."
LEINSTER: C Bridgeman (Capt. St Aidans), T Colvin (St Peters Dunboyne), D O'Donnell (Vice Capt, Scoil Catriona), R Maguire (St Joseph's Cabra/Deaf), S O'Sullivan (St Aidans), J Reilly (Institute Ed), C McCarthy (St Laurances Loughlinstown), C Kelleghan (Coolmine), H Lawlor (Blackrock College), D Murphy (St Mac Darras), B Lawlor (Blackrock College), E O'Meara( Pobalscoil Neasain), C Colvin (St Peters Dunboyne), L Harris (Colaiste Choilm, Swords), Coach Sean Kenna (St Peters, Dunboyne) Assistant Coach: G Dunne (St Joseph's /Deaf).
REFEREES: S O'Brien, B O'Dwyer, T Farrelly.
Tournament Organiser: B Fitzpatrick (St Joseph's /Deaf)