It also left Ulster Rugby as the sole team still able to boast four from four ahead of the final two rounds of matches in the New Year.

Leinster, the reigning Amlin Challenge Cup champions, were playing their 125th tournament match but suffered only their second defeat from their last 17 home contests.

The victory represented a massive turnaround for the Saints following their 33-point defeat in front of their home fans in Round 3, this time outscoring the triple former Heineken Cup champions 2-0 in tries.

And it was Wales and British & Irish Lions star George North who got the first and made sure the Saints made the sort of start that would help put a damper on a vibrant and expectant Dublin crowd.

Teenager Tom Collins had Rob Kearney in trouble with the Saints wing’s pure pace on the turn and the Leinster man impedes him short of the line.

Northampton opted to kick for touch, making a clear statement of intent, and they followed that up brilliantly with North running a great line for a superb try and first blood to the visitors.

Steve Myler added the conversion but Ian Madigan got Leinster up and running with a 10th minute penalty as the contest really came alight.

And the Saints were unrecognisable from the side humbled 40-7 at Franklins Gardens the previous weekend – “we were embarrassed out there and came second best,” confessed Director of Rugby Jim Mallinder – this time taking the game to Leinster at every opportunity.

Myler was off target with a penalty goal chance just before the break but the action so far had promised another thrilling, nerve-tingling 40 minutes to come.

And Madigan took just a few moments of those 40 remaining to land a second penalty goal and cut the deficit to just a single point, Saints the first to start ringing the changes with the introductions of Tom Mercy and Kahn Fotuali’i.

Leinster soon followed with Michael Bent, Kevin McLaughlin, Martin Moore and Zane Kirchner all joining the action and reinforcing Leinster’s challenge but it was the boot of Myler that had the next say with a penalty that took them into double figures when, having turned down the possibility of three points for the possibility of five a couple of times, Dylan Hartley points to the posts on this occasion and Myler does the business.

However, those three points are cancelled out just eight minutes later with Madigan’s third successful penalty goal to set up a pulsating grandstand finish.

Nerves were clearly jangling as Myler was off target with a penalty goal chance for Saints but Fotuali’I shoeds calmness itself to drop a glorious goal with just two minutes to go after some telling mauling by his pack.

It was left to Jamie Elliott to provide the icing on the Saints cake with their second try at the death and although Myler could not land the conversion, the length of the field Elliott try had denied Leinster even a losing bonus point.