By Bryn PalmerBBC Sport at the Millennium Stadium, Cardiff
Leinster (6) 33
Tries: Sexton (2), Hines
Cons: Sexton (3)
Pens: Sexton (4)
Northampton (22) 22
Tries: Dowson, Foden, Hartley
Cons: Myler (2)
Sexton contributed 28 points for Leinster
Leinster were crowned European champions for the second time in three years after the greatest comeback in Heineken Cup final history at Cardiff's Millennium Stadium.
First-half tries from Phil Dowson, Ben Foden and Dylan Hartley had put underdogs Northampton within sight of an upset as they led 22-6 at the interval.
But the 2009 champions launched a devastating blitz of 27 unanswered points inside 26 minutes to overrun the Saints, Jonathan Sexton grabbing two tries and Nathan Hines adding a third.
Sexton added 18 points with the boot for a 28-point personal haul to claim the man-of-the-match award as Leinster brought the elite band of clubs who have won the Heineken Cup twice or more up to five.
The Dublin-based team join provincial rivals Munster, English duo Leicester and Wasps, and Toulouse, who are out on their own with four titles.
But Leinster, who could complete a European and domestic double with a Magners League final against Munster next Saturday, look well placed to add to their collection after this stunning triumph.
They were a ragged bunch for the first period, overpowered at the scrum, dominated at the breakdown, and flimsy in defence.
But after a rip-snorting opening to the second half that brought Sexton's first try within four minutes of the resumption, they never looked back.
Saints, perhaps feeling the effects of last weekend's punishing Premiership semi-final defeat by Leicester, were outmanoeuvred in a dramatic transformation and faded badly, seemingly powerless against the swarming blue tide.
Not that the English side showed any sides of fatigue in a super-charged opening passage of play lasting two minutes and 17 seconds.
Centre James Downey cut inside Gordon D'Arcy to launch a Saints attack that went through umpteen phases until a Hartley knock-on brought the first pause in the action.
Their pack appeared to have the edge in the first two scrums, confirmation of which came in the third set-to after Jonathan Sexton's huge clearance kick rolled inches too long, allowing Northampton a scrum back inside Leinster 22.
BRYN PALMER'S BLOG
“Leinster look a good bet to go on and win more Heineken titles in the years to come”
Referee Romain Poite called captains Leo Cullen and Hartley together to lay down the law, and Saints drove the scrum, getting the penalty, but Roger Wilson, Paul Diggin and Lee Dickson carried the ball before Calum Clark sent Dowson charging over in the left corner.
Stephen Myler added a superb conversion from the touchline, and Saints were invigorated. Christian Day stripped D'Arcy of the ball, number eight Wilson burst clear from the back of a scrum, but Clark was pinged at the breakdown and Sexton stroked over a superb penalty to make it 7-3.
Saints prop Soane Tonga'uiha had proffered the opinion beforehand that it might take until the last five minutes to earn any scrum dominance, but he and his cohorts splintered the Leinster pack for a second time to earn another penalty after 20 minutes that Myler nudged over from 40m.
Leinster probed dangerously and Shane Horgan cut a fine angle through the Saints midfield. Sean O'Brien released Brian O'Driscoll and the celebrated centre pinned back his ears towards the right corner, only to be cut down metres short by Foden.
Saints then mullered Leinster again at the scrum, but by the next set-piece found themselves a man down after South African prop Brian Mujati was sin-binned for cynically holding back Cian Healy.
Remarkably, Mujati's absence barely registered with Saints, who extended their lead without him. Sacrificing Clark, Tom Mercey came on at prop and the East Midlanders proceeded to push back their opposite numbers even with seven men, earning a third scrum penalty.
Cullen felt obliged to seek clarification from Poite at that point, and he was similarly bemused moments later when Saints won the next scrum against the head deep into Leinster territory.
Myler's initial dart was held up short, but scrum-half Dickson spun the ball out left and Jon Clarke sent Foden arcing round O'Driscoll's tackle to score and send the Saints' fans into delirium. Myler added the extras and Saints were 17-3 to the good after 32 minutes.
A high tackle on D'Arcy allowed Sexton to reduce the deficit to 11 points, but Leinster knocked on at the kick-off and Saints finished the half battering away at the Leinster line, Clarke and Chris Ashton - twice - both held up short. But Saints surged again, and Hartley was adjudged - after consultation with the video referee - to have been driven over for their third try.
Myler saw his conversion attempt come back off an upright, but Leinster's players, lined up on their own try-line, looked understandably shell-shocked.
Replacing Kevin McLaughlin with Shane Jennings at flanker for the second half, the Irish side needed an instant riposte, and they got it within four minutes.
O'Driscoll picked up a loose ball and burst through, Jamie Heaslip and Isa Nacewa were held short, but when the ball was moved swiftly left, Eoin Reddan sent Sexton over for a smart finish.
The fly-half saw his conversion bounce over off an upright and with their tails up, Leinster's threat was all-consuming. After another relentless period of pressure, D'Arcy - with Wilson and Diggin getting boots and arms underneath him, could not ground the ball in the right corner, after a lengthy review process by the television official.
Saints survived that decision, but could not resist the unstoppable head of steam Leinster had built up.
After 53 minutes, Sexton battered his way over after another blue onslaught, converting his own try to bring Leinster within two points.
Suddenly the roles were reversed. Foden dropped a high ball, and Leinster's fired-up forwards took great delight in earning a penalty at the resultant scrum.
When Sexton sent it flying between the uprights, the 2009 champions had transformed a 16-point deficit into a one-point lead within 17 minutes.
Immediately the Saints line was under siege again, and desperate defence saw Dowson, infringing at a ruck, sent to the sin-bin.
Sexton potted the resultant penalty, and was converting Leinster's third try minutes later when Scottish lock Hines, in his last game before departing for French club Clermont Auvergne, plunged over.
Saints sent on four replacements in a bid to stem the blue tide, but one of them, Shane Geraghty, was promptly engulfed by four tacklers and had no option but to concede a penalty. To general astonishment, Sexton missed his first kick of the evening.
Resistance looked futile, but Foden launched one dashing counter-attack from deep that Ashton carried on, only for Leinster to turn it over.
After that, both coaches emptied the benches to give all the players a taste of the final atmosphere, but there was only one team enjoying it by then.
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