Northampton gained revenge for last year's two Heineken Cup defeats against Llanelli Scarlets with a dominant display at Franklin's Gardens.
HEINEKEN CUP POOL 3
Northampton: (18) 25:
Tries: Fox, Human 2.
Cons: Grayson 2.
Pens: Grayson 2.
Scarlets: (3) 3:
Pen: A Thomas.
Flanker Darren Fox and wing Wylie Human, with a brace, scored tries, while Paul Grayson kicked 10 points.
But Kiwi full-back Bruce Reihana was Saints' star and his open play with wing Ben Cohen was a constant threat.
The Welsh side had a solitary Arwel Thomas penalty to their name and remain winless in Pool Three after two rounds.
The Scarlets did the double over Northampton in Europe last year and signalled their early intent to do the same again.
Full-back Barry Davies darted down the right wing and the Welsh forwards rumbled on to earn a penalty in front of the posts, Thomas slotting the conversion.
But that was to be their only score of the game as Saints skipper Corne Krige and Andrew Blowers led the fightback.
Two penalties from Grayson made it 6-3 to the Saints, who then struck twice in quick succession moments before half-time to devastate their visitors.
Reihana and Cohen were again quicker in mind and then foot to take a swift throw-in and counter-attack, sending flanker Fox crashing over for a converted try.
Thomas then fluffed a chance to claw back three points for Scarlets and from his missed kick, Northampton marched upfield and created space on the right for Human to race over.
Trailing 18-3 at the break, Scarlets coach Gareth Jenkins reacted by ringing the changes, including sending Gareth Bowen on at fly-half in place of Thomas.
The Scarlets improved, with Scott Quinnell to the fore, but spurned their first kickable penalty after 58 minutes, opting for a set move instead of taking the points on offer.
Grayson's tactical kicking kept the Scarlets on the back foot but they had to wait until five minutes from the end for the decisive score, Human cutting a brilliant angle for his second try after Reihana again broke through.
Only the lack of a fourth try for a bonus point prevented it being a perfect afternoon for Saints, who now face French giants Toulouse.
The Scarlets' miserable season continues and they must win in Glasgow next time to stand any chance of clawing their way back into contention.
Northampton: B Reihana; W Human, M Stcherbina, C Hyndman, B Cohen; P Grayson, M Robinson; T Smith, D Richmond, C Budgen, M Lord, D Browne, D Fox, C Krige (capt), A Blowers.
Replacements: J van Wyk, B Sturgess, E O'Donoghue, G Seely, J Howard, S Drahm, A Vilk.
Scarlets: B Davies; G Evans, M Watkins, M Taylor, T Selley; A Thomas, D Peel; I Thomas, M Rees, J Davies, A Jones, C Wyatt, D Jones, S Easterby (capt), S Quinnell.
Replacements: P John, C Hawkins, B Griffiths, G Thomas, M Phillips, G Bowen, S Finau.
Referee: Alain Rolland (Ireland).