|London Irish (6) 25|
|Try: Lewington, Bell, McNally Con: Bell, Tonks Pens: Bell 2|
|Northampton (26) 40|
|Tries: Groom, Horne 2, Hayward, North, Reinach Cons: Mallinder 5|
Northampton made it three successive Premiership wins as they eased to victory at London Irish.
Saints had a bonus point wrapped up before the break through Nic Groom's score, two tries from Rob Horne and another from Mike Hayward.
Irish threatened a comeback when Alex Lewington's try made it 26-13.
But George North made the game safe for the visitors before Tommy Bell and Josh McNally scored late on for Irish either side of Cobus Reinach's try.
Northampton's victory, which followed their back-to-back wins over Leicester and Bath, lifts them to third in the table, level on points with Saracens, who handed Saints their only defeat so far on the opening day of the season.
That loss in the first half of the Twickenham double header was followed by London Irish's thrilling win over Harlequins, but the Exiles have now lost all three of their subsequent matches to sit second from bottom.
Northampton did much of the hard work in the opening five minutes when they scored twice.
Groom finished off a fine team move and was swiftly followed in by Horne, who powered his way over after the Saints pack turned a lineout over.
Horne showed good strength to score his second and when Hayward drove over at the back of a maul, Northampton appeared to have the game won within 30 minutes.
However, Bell kicked his second penalty on the stroke of half-time, and when Lewington raced past three defenders to score Irish's first try soon after the restart, a comeback did not seem out of the question.
But Saints replied immediately through North to re-establish a 20-point lead, and although Bell and McNally added further tries for the home side either side of Reinach's effort, they came too late to affect the outcome.
London Irish director of rugby Nick Kennedy:
"For the third week in a row we gave ourselves a mountain to climb against a very good team. Our overall work needs to improve.
"When we looked after the ball we looked dangerous, but we kept coughing up the ball which was frustrating.
"We've conceded a lot of points but we always knew how hard it would be. We knew it would be a tough season."
Northampton director of rugby Jim Mallinder:
"It was a little bit end-to-end and we couldn't relax until it was over. It was good to score 40 points away from home and get the bonus point.
"The start was exactly what we talked about - being direct and being physical. We scored two cracking tries, one from counter-attack and Rob Horne's finish was really pleasing.
"We were a little loose at times and maybe a little guilty of overplaying. But some of our good attacking play led to some good tries and you don't want to stop that natural instinct of playing."
London Irish: Bell; Lewington, Tikoirotuma, J. Williams, Nagala; Marshall, McKibbin; Franks, Porecki, du Plessis, van der Merwe, De Chaves, McNally, Gilsenan, Cowan.
Replacements: Paice, Elrington, Hoskins, Paulo, Schatz, Steele, Tonks, Ojo.
Northampton: Tuala; North, Horne, Burrell, Collins; Mallinder, Groom; Waller, Haywood, Hill, Paterson, Ribbans, Lawes, Gibson, Dickinson.
Replacements: Marshall, Ma'afu, Brookes, Day, Nutley, Reinach, Grayson, Foden.
Referee: Matt Carley (RFU)