|Heineken Champions Cup Pool One|
|Northampton (16) 16|
|Tries: Tuala Con: Biggar Pens: Biggar 3|
|Leinster (19) 43|
|Tries: Lowe, Ruddock, Porter, Healy, R Byrne, McGrath, E Byrne Cons: Sexton 2, R Byrne 2|
Last season's runners-up Leinster remain top of Pool One after a bonus-point Champions Cup win at Northampton.
Leinster's James Lowe scored first before Northampton's Ahsee Tuala crossed in a lively start.
Rhys Ruddock claimed Leinster's second try and the Irish side led at the break thanks to Andrew Porter's score.
The visitors then dominated the second half with tries from Cian Healy, Ross Byrne, Luke McGrath and Ed Byrne sealing victory.
Leinster power ahead in second half
Both sides were unbeaten in the competition so far but, when Jordan Larmour broke loose to set up Lowe's score in the third minute, it looked as if it would be a tough day for Northampton.
The hosts initially held their own and hit back soon after, opening up Leinster's defence to give full-back Tuala the chance to go over in the left corner.
Biggar's impressive conversion from the touchline evened the scores, before the fly-half took Northampton into the lead with a penalty.
Then, another scything run from Larmour helped Jamison Gibson-Park to within a few metres of the tryline, but flanker Ruddock was the man who drove over to score.
Leinster's penalty count began to get the better of them - they conceded six in the first half - and two kicks from Biggar gave Northampton a two-point lead.
The tables turned a fifth time though, as Leinster prop Porter powered over from the base of a ruck just before half-time.
And the four-time champions gathered momentum following a score from Healy after the break, with the conversion coming from Ross Byrne because Johnny Sexton had left the field with a knee injury.
Byrne soon followed this up with a try of his own after a break from Caelan Doris before McGrath and Ed Byrne crossed from close range to take Leinster's try count to seven.
Leinster now have a five-point lead over Northampton at the top of Pool One, with Lyon third following a 28-0 victory against Benetton.
The sides will face each other again at the Aviva Stadium in Dublin on Saturday, 14 December.
A 'reality check' for Northampton - what they said
Northampton director of rugby Chris Boyd: "We were in the game at half-time but I got the feeling they probably had more petrol left in the tank than we did. It was a reality check.
"It's a learning for us that there's another level of physicality and fitness required if we're going to compete with teams like Leinster. We have to be optimistic that we can close the gap."
Leinster head coach Leo Cullen: "We're just trying to build cohesion with the guys coming back from the World Cup and that's taking a bit of time.
"This was a positive step but we'll get better each week and continue to improve."
Northampton: Tuala; Collins, Proctor, Hutchinson, Naiyaravoro; Biggar, Reinach; Waller, Haywood, Painter, Moon, Ratuniyarawa, Wood, Gibson, Harrison
Replacements: Van Vuuren, Van Wyk, Hill, Coles, Ludlam, Tupai, Grayson, Francis
Leinster: Larmour; Kearney, Ringrose, Henshaw, Lowe; Sexton, Gibson-Park; Healy, Kelleher, Porter, Toner, Ryan, Ruddock, Van der Flier, Doris
Replacements: Tracy, E Byrne, Furlong, Fardy, Deegan, McGrath, R Byrne, Kearney