Scarlets made it four wins out of four in the PRO12 after they saw off Leinster on Friday, with DTH van der Merwe (2) and James Davies scoring.
Van der Merwe's first-half touchdown, alongside a try from Davies, gave the Welsh region a deserved 15-0 lead at the break.
The winger added his second after half-time before a Steve Shingler penalty took the game out of the opposition's reach.
Leinster managed to cross the whitewash through Isa Nacewa and James Tracy, but the Scarlets secured their fourth successive league victory.
Wayne Pivac's men have enjoyed an excellent start to the campaign and their first-half performance showed why. By contrast, the Irish province were disappointing and deservedly went 8-0 behind after nine minutes.
The Scarlets dominated possession and, after Shingler had kicked an early penalty, the hosts put together a fluent attack which resulted in Davies going over.
After that effort Leo Cullen's side finally began to exert some pressure, although they failed to convert it into points. Instead, the home team took advantage of some loose handling by the visitors and Van der Merwe, who impressed for Canada at the World Cup, intercepted a stray pass to scamper clear.
This time, Shingler was on target with the conversion and his team led 15-0 at the interval.
Cullen needed a response from his charges but the match continued in the same vein with Leinster struggling to deal with their opponents' pace and intensity. Under duress, it was no surprise to see the three-time European Cup winners receive a yellow card when Noel Reid was sent from the field for 10 minutes, but they displayed determination following that infringement.
Leinster resisted the initial stages of that sin-binning with some excellent last-ditch defence before they finally succumbed to the barrage when Van der Merwe crossed the whitewash.
Back to 15, the away side managed to muster a score, one which was both superbly created and taken, with Nacewa the recipient of an outstanding move. Tracy then went over, but it proved to be just a consolation effort as the Scarlets took the win.
Tries: J Davies, Van der Merwe 2
Con: Shingler 2
Pen: Shingler 2
Tries: Nacewa, Tracy
Con: McFadden 2
Scarlets: 15 Aled Thomas, 14 Hadleigh Parkes, 13 Regan King, 12 Gareth Owen, 11 DTH van der Merwe, 10 Steven Shingler, 9 Aled Davies, 8 John Barclay (c), 7 James Davies, 6 Aaron Shingler, 5 Tom Price, 4 George Earle, 3 Peter Edwards, 2 Kirby Myhill, 1 Rob Evans.
Replacements: 16 Ryan Elias, 17 Phil John, 18 Will Taylor, 19 Tom Phillips, 20 Jack Condy, 21 Rhodri Williams, 22 Dan Jones, 23 Tom Williams.
Leinster: 15 Isa Nacewa (c), 14 Fergus McFadden, 13 Colm O'Shea, 12 Noel Reid, 11 Garry Ringrose, 10 Ross Byrne, 9 Isaac Boss, 8 Dan Leavy, 7 Josh van der Flier, 6 Dominic Ryan, 5 Tom Denton, 4 Ross Molony, 3 Marty Moore, 2 Bryan Byrne, 1 Michael Bent.
Replacements: 16 James Tracy, 17 Peter Dooley, 18 Jamie Hagan, 19 Tadhg Beirne, 20 Tony Ryan, 21 Luke McGrath, 22 Cathal Marsh, 23 Mick McGrath.
Referee: Peter Fitzgibbon (Ireland)
Assistant referees: Wayne Davies (Wales), Greg Morgan (Wales)
TMO: Tim Hayes (Wales)