Northampton suffered their second Heineken Cup defeat on the bounce after losing to the Scarlets 28-23 at Franklin's Gardens on Friday.
The Welsh outfit ensured they headed home with a bonus-point win thanks to first-half tries by Liam Williams, Aaron Shingler and Matt Gilbert while Rhys Priestland grabbed another after the break.
The Wales fly-half also kicked four conversions in a virtuoso display, with his boot causing the Saints no end of problems throughout the match.
Last season's beaten finalists managed to secure a bonus point in defeat, courtesy of late tries to George Pisi and Tom Wood. But that will be of little consolation to director of rugby Jim Mallinder, who was this week linked with the England job.
The visitors took the lead with barely two minutes up on the clock when scrum-half Gareth Davies made the break before feeding to full-back Williams, who kicked ahead and grounded the ball. Priestland added the extras.
Northampton got themselves on the board when Ryan Lamb slotted over a simple penalty after the Scarlets were penalised at the breakdown.
However the men in red struck again straight from the restart as flank Shingler picked up a loose ball and scored in the corner with Priestland once again converting.
Lamb knocked over another penalty in the 23rd minute but it was the Scarlets who continued to come forward as the match approached the half-hour mark.
The hosts did come into their own towards the end of the half and a Lamb penalty after a scuffle at a lineout cut the gap to five.
But one more lapse at the back from the hosts would cost them dear as full-back Pisi spilled a high kick from Priestland and the visitors pounced, with Gilbert eventually crossing for try number three.
Priestland converted to make it 21-9 at the break.
Northampton needed a fast start to the second half but were instead forced to soak up more pressure in the opening stages, with Priestland continuing to test the Saints' back three with booming kicks.
The Scarlets suffered a blow when flanker Jonathan Edwards was shown a yellow card for slowing down the ball, but Lamb hit the upright with the insuing penalty.
And moments later the contest was effectively killed off as a knock-on from England wing Chris Ashton was kicked ahead by Priestland and then again by rampaging George North, with the former touching down to complete an incredible break.
Pisi got one back in the 68th minute to give Northampton a faint glimmer of hope, but the deficit proved far too much to overcome.
The match did end on a slightly concerning note for the Scarlets, however, as North hobbled off after being manhandled in a ruck by Ashton and Wood scored a breakaway try under the posts.
Tries: Pisi, Wood
Cons: Lamb 2
Pens: Lamb 3
Tries: Williams, Shingler, Gilbert, Priestland
Cons: Priestland 4
Northampton: 15 Ben Foden, 14 Chris Ashton, 13 Jon Clarke, 12 James Downey, 11 Vas Artemyev, 10 Ryan Lamb, 9 Lee Dickson, 8 Roger Wilson, 7 Tom Wood, 6 Calum Clark, 5 Mark Sorenson, 4 Courtney Lawes, 3 Brian Mujati, 2 Dylan Hartley, 1 Soane Tonga'uiha.
Replacements: 16 Mikey Haywood, 17 Alex Waller, 18 Paul Doran-Jones, 19 Samu Manoa, 20 Phil Dowson, 21 Martin Roberts, 22 Steve Myler, 23 George Pisi.
Scarlets: 15 Liam Williams, 14 George North, 13 Scott Williams, 12 Jonathan Davies, 11 Sean Lamont, 10 Rhys Priestland, 9 Gareth Davies, 8 Ben Morgan, 7 Jon Edwards, 6 Aaron Shingler, 5 Damian Welch, 4 Sione Timani, 3 Rhys Thomas, 2 Matthew Rees, 1 Iestyn Thomas.
Replacements: 16 Ken Owens, 17 Phil John, 18 Rhodri Jones, 19 Lou Reed, 20 Matt Gilbert, 21 Rhodri Williams, 22 Stephen Jones, 23 Daniel Evans.
Referee: Peter Fitzgibbon (Ireland)