Alex Waller's second-half try was enough for Northampton to overcome the Scarlets for a 15-11 Champions Cup win at Franklin's Gardens.
Waller's try came just five minutes after Gareth Davies had given Scarlets a surprise second-half lead and Saints were able to hold on for a vital win.
While the scoreline was close, Northampton were deserved victors, and could have won by more, but the Scarlets' defence held up well.
Having endured a tough start to the season in the Premiership, Saints meant business with an early try from Ken Pisi, but led just 7-6 at the break, George North having been sin-binned for a stamp which cost them one try.
Davies went over early in the second half, but Waller responded from a maul, before JJ Hanrahan gave his team some breathing space with a late penalty.
Northampton flew out of the blocks and scored the game's opening try after just six minutes. In control at scrum-time and making ground with ball in hand, they went in front when Hanrahan beat two men before finding his Samoan winger, Pisi, who had the pace to race over. The Irish fly-half converted to make it 7-0.
The Scarlets struggled for any possession in the early stages, but did at least get on the board after 14 minutes when they finally got some ball and Jamie Gibson was penalised for slowing the ball after DTH van der Merwe and then Aaron Shingler had been stopped just short. Steven Shingler, who had a poor night with the boot, slotted from in front.
After a missed kick from Shingler, Saints thought they had their second try. Pisi made a great break and good interplay between Ben Foden and North saw Luther Burrell over. As Hanrahan prepared to take the conversion, a stamp from North was spotted on the big screen. The Wales winger had reacted badly to being held by Michael Tagicakibau, and was sin-binned for his stamp on the winger's shoulder.
The stamp came before the try, so that was also disallowed, but Saints did well not to concede any points, and could have even moved further in front only for Hanrahan to miss a couple of kicks.
Late in the half Tom Wood was penalised for not rolling away at a ruck, and Shingler took advantage to pull the Scarlets back to within a point at the break.
Having been outplayed for much of the first half, it was the Scarlets who took the lead in the second half, with a fine score from Davies. After a break through by Aled Thomas, he found the scrum-half on his shoulder, and despite a hint of a forward pass, Davies had the pace to sprint over.
Shingler missed the conversion and four minutes later Saints were back in front. A fine driving maul ended with Waller going over as Scarlets were incapable of stopping the Northampton pack.
Hanrahan missed the touchline conversion and it remained a one-point game.
Northampton had been warned a number of times for slowing the ball down at ruck-time, an area where they had also enjoyed a lot of success. Romain Poite finally lost his patience with 20 minutes to go, and Gibson was binned as he failed to roll away at a ruck.
Gibson's absence made no difference to Northampton's scrum domination though, and with 12 minutes left, a big effort from Paul Hill earned Saints three more points from the boot of Hanrahan.
The Scarlets had their chances to take advantage of the extra man, but couldn't find a way through, and one penalty attempt from Thomas came back off the post just before Gibson returned.
They did have another opportunity and had to settle for a losing bonus point in the end.
Tries: Pisi, Waller
Yellow Cards: North, Gibson
Pens: Shingler 2
Northampton: 15 Ben Foden, 14 Ken Pisi, 13 George Pisi, 12 Luther Burrell, 11 George North, 10 JJ Hanrahan, 9 Lee Dickson (c), 8 Sam Dickinson, 7 Tom Wood, 6 Jamie Gibson, 5 Christian Day, 4 James Craig, 3 Kieran Brookes, 2 Mikey Haywood, 1 Alex Waller.
Replacements: 16 Matti Williams, 17 Ethan Waller, 18 Paul Hill, 19 Michael Paterson, 20 Teimana Harrison, 21 Kahn Fotuali’i, 22 Stephen Myler, 23 Ahsee Tuala.
Scarlets: 15 Aled Thomas, 14 Michael Tagicakibau, 13 Gareth Owen, 12 Hadleigh Parkes, 11 DTH van der Merwe, 10 Steven Shingler, 9 Gareth Davies, 8 John Barclay (c), 7 James Davies, 6 Aaron Shingler, 5 Maselino Paulino, 4 Jake Ball, 3 Peter Edwards, 2 Emyr Phillips, 1 Rob Evans.
Replacements: 16 Kirby Myhill, 17 Phil John, 18 Will Taylor, 19 Tom Price, 20 Lewis Rawlins, 21 Aled Davies, 22 Regan King, 23 Tom Williams.
Venue: Franklin's Gardens
Referee: Romain Poite (France)
Assistant referees: Tual Trainini (France), Pierre Brousset (France)
Television match official: Eric Gonthier (France)