Scarlets (0) 7
Try: J Davies Con: S Jones
Leinster (22) 32
Tries: Horgan, Nacewa, Berne, O'Brien Cons: Berne 3 Pens: Berne 2
Shane Horgan rounds Ken Owens on his way to Leinster's opening try
Heineken Cup holders Leinster produced the form of champions in a memorable bonus point win at the Scarlets.
It was their second away win, having triumphed at Brive, following a 12-9 opening round defeat by London Irish in Dublin.
Leinster led 22-0 at the break thanks to tries from Shane Horgan, Isa Nacewa and Shaun Berne and another followed in the second half from Sean O'Brien.
Jonathan Davies scored the hosts' try as they rallied after the break.
Leinster fly-half Berne gave an outstanding display after moving from centre to the number 10 jersey in the absence of Ireland's rising star Jonathan Sexton.
Berne, making his first full appearance since joining from Bath in the summer, scored the third of his side's tries and contributed deft touches as well as three conversions and two penalties for a 17-point haul.
The Scarlets threw down the gauntlet by taking the game to the Irish province from the first whistle and Leo Cullen's side more than accepted the challenge to leave the hosts with an uphill battle to qualify for the quarter-finals.
Some weak defence did not help the hosts' cause as Shane Horgan waltzed through for the opening score after four minutes from near half way.
Berne spotted Horgan had some space out wide, the wing still had a lot to do as he cut past wing Andy Fenby before leaving hooker Ken Owens in his wake and gliding past Daniel Evans' inside shoulder.
Berne converted and added a penalty after 19 minutes.
Brian O'Driscoll earned a warning from English referee Chris White after tackling Evans high as the full-back took a high ball.
But the Leinster talisman proved his footballing talents moments later by helping Isa Nacewa reach the line.
Berne again converted that 22nd-minute score and seven minutes later went over himself after some sharp play from Eoin Reddan.
Scrum-half Reddan took a line-out quickly after O'Driscoll forced fly-half Jones into touch and Nacewa linked with Rob Kearney who sent Berne over at the corner to give the visitors their 22-0 lead at the break.
The Scarlets launched a spirited fight-back after the restart, opting to kick for line-outs and drive from close range as they put Leinster's pack under intense pressure.
A reward came at the second attempt as centre Jonathan Davies crashed through Gordon D'Arcy's attempted tackle, drove past Berne and brushed off O'Driscoll as he powered over.
Jones converted and the pressure on Leinster again told after the Scarlets launched another assault.
This time lock Nathan Hines was sin-binned for killing the ball, but the visitors regained some composure to give Kearney a stab at a long-range penalty that he sent wide.
The encounter reached boiling point in the 56th minute as Scarlets centre Sean Lamont's shoulder-charge in midfield on Nacewa almost sparked a mass brawl amid the pushing and shoving that ensued.
Lamont earned a yellow card for his sin and Berne kicked the penalty to help calm Leinster's nerves.
The visitors underlined their superiority in the 72nd minute as Jamie Heaslip provided the final pass for flanker Sean O'Brien to crash over sandwiched between half-backs Jones and Martin Roberts.
Scarlets: Evans; Fenby, Lamont, J Davies, L Williams; S Jones, Roberts; I Thomas, Owen, Manu, Reed, Day, Easterby, Pugh, Lyons (capt).
Replacements: Knoyle for Roberts (73), John for I Thomas (66), Phillips for Owen (77), Cooper for Day (71), McCusker for Pugh (77).
Not Used: Corsi, Priestlend, Maule.
Yellow card: Lamont, 56
Leinster: R Kearney; Horgan, O'Driscoll, D'Arcy, Nacewa; Berne, Reddan; Healy, Fogarty, van der Linde, Cullen (capt), Hines, McLaughlin, O'Brien, Heaslip.
Replacements: McFadden for O'Driscoll (73), Dempsey for Berne (76), O'Donohoe for Reddan (74), Wright for Healy (73), Jackman for Fogarty (71), Ross for van der Linde (51), O'Kelly for Cullen (77). Not Used: S Keogh.
Yellow card: Hines, 48
Ref: Chris White (RFU).