In Dublin they may put it down to a bit of a slow start, but to everyone else this was an astonishing comeback, a final turned around in the second half, after a full first half of being made to look silly. For the record, it was a Heineken Cup final that broke the record for most tries – six – and a personal tally of 28 points for Jonathan Sexton, not quite enough to beat Diego Domingo's 30 in 2001, but enough to make him the man of the match, the orchestrator of a sensational swing.

To appreciate the brilliance of the second period it may be necessary to relive Leinster's hell in the first. Sexton's first contribution was to build some wind factor into an early kick downfield, which would have been fine if the roof had not been closed. The ball bounced dead and Northampton had a chance to settle into a scrum in the Leinster 22.

They budged not an inch, allowing Paul Diggin to take the ball on the unconventional left-hand side of the scrum. The wing fed the first wing forward, Calum Clark, who threaded a meticulous one-handed pass to the second, Phil Dowson.

Leinster's single source of comfortable possession was Shane Horgan chasing restarts, which is not the kind of thing you aim to have as a strategy. The wing did his job splendidly against Diggin and the taller James Downey, but every restart meant Northampton had scored, on the second occasion with a Steve Myler penalty.

Even more disturbing than being inconvenienced at the scrum was the sight of Brian O'Driscoll struggling on his gammy knee. He was put clear after more fine work by Horgan, with only Ben Foden to beat. England's full-back showed him the outside and hauled Ireland's icon down without compassion.

And it grew even worse when the gift of a yellow card, shown to Brian Mujati for pulling Cian Healy's shirt off the ball, turned out to be a spur only to Northampton. A reduction in the opposition ranks was meant to work in Leinster's favour. Instead they were pushed off the ball.

At the next scrum they lost the ball on their own feed and Foden barged between Horgan and O'Driscoll. The only words that applied to O'Driscoll at this stage were the old adage: never play when you're injured. The half ended with Mujati returning just after Nathan Hines dropped a restart after what looked like a crumb of consolation, Sexton's second penalty. Back to 15, Northampton belted their way close to the line and Hartley was awarded a try. The score was 22-6. This was over.

Sexton in the changing room at half-time, according to O'Driscoll, was a "man possessed". This was not yet done and dusted. Something of the outside‑half's fury rubbed off on O'Driscoll and suddenly, four minutes into the second half, he was his old self, making ground for Isa Nacewa to charge close to the line. Sean O'Brien continued the momentum and Sexton took the pass to score.

Gordon D'Arcy was held up over the line by Paul Diggin and the wing managed an act of contortion to place a knee under the centre to prevent him from grounding the ball. It was only a temporary respite, for the Leinster team were now gripped by a fever. Sexton combined with James Heaslip, took the return pass from the No8 and in the space of 10 minutes the gap was down to two points.

Those who had won the first half were now losing the second badly. Foden dropped the ball, Leinster drove the scrummage to win themselves a penalty and Sexton put them in front. Nacewa caught a high kick acrobatically, Healy and O'Brien scattered tacklers and there was now only one team in this final.

Dowson was shown a yellow card as Leinster powered forward yet again and this time the disadvantage could not be reversed. Sexton kicked another penalty for the offence and four minutes later, Hines marked his farewell from the province by stretching out for a try after more blasting by O'Brien, the hooker Richardt Strauss and, after a quite superb one-handed catch on the hoof,Ω by the second-row Leo Cullen.

It was all over now. Northampton tried to rally and Chris Ashton was put into open space. Nacewa crashed him to the floor and the England wing limped off. It was an unhappy end to the unhappiest of halves for the Saints. Their past eight days, in fact, have been pretty miserable.

Leinster have nothing to feel sorry about, apart from perhaps giving their supporters palpitations. By the end it was a breeze and the players had already been forgiven. Quite how the scrum mended itself, quite how drivers that had been tossed around in the first half became bulldozers, quite where the gaps came from are questions that will haunt Northampton for a long time. Leinster will say that it just took a bit of time to find their rhythm.

Or perhaps they will admit that they frightened themselves rigid and had to follow Sexton and become players possessed. Whatever, if they can remember what they did at half-time it is worth bottling and selling.

Their triumph was mythical enough to send Ireland's economy from red to black.