Scarlets wing Dafydd James holds off Denis Hickie to score
Scarlets 33 (27)
Tries: D James 2, I Afeaki, King.
Cons: S Jones 2.
Pens: S Jones 3.
Leinster 21 (7)
Tries: D Hickie 2, L Fitzgerald.
Cons: F Contepomi 3.
Llanelli Scarlets raised themselves to the top of the Magners League in style with an outstanding first-half display of running rugby against Leinster.
Dafydd James, twice, Inoke Afeaki and Regan King all crossed to earn Scarlets a bonus point within the first quarter.
Leinster came back strongly, with wing Denis Hickie grabbing two tries including a long-range interception.
Trevor Hogan went over for the Irish side's third try, but Stephen Jones' boot kept Scarlets out of reach.
Leinster were swept aside in an irresistible opening by their hosts that saw Scarlets run in four tries in the first quarter.
It took James just 70 seconds to open his account, as a series of drives sucked in Irish defenders to create space for the right wing to take Simon Easterby's pass and go in at the corner.
Jones missed the conversion, but made no mistake with an easier chance just three minutes later from Afeaki's try.
Turning over Leinster ball just inside their own half, Scarlets forwards and backs combined in a surging counter-attack that went through a dozen pairs of hands before the Tongan lock stretched over.
The third was almost as good, Regan King's half-break sending Matthew Watkins through a gap before Ceiron Thomas went bounding towards the line.
An excellent cover-tackle from Kieran Lewis downed the Scarlets full-back just short, but James was in support to claim his second try.
Jones added a penalty kick to stretch the lead to 20-0, earning good-natured boos from the Stradey Park crowd.
But the fans need not have worried as a fourth try and bonus point soon followed, Dwayne Peel taking Alix Popham's flick from a five-metre scrum and sending King under the posts for another seven points.
Hickie gave Leinster something to build on by intercepting Popham's loose pass to race 50 metres under the posts, Felipe Contepomi converting, but the Irish trailed 27-7 at half-time.
With Scarlets looking so dangerous with ball in hand, Leinster came out determined to keep it away from the Welsh.
A series of drives took Leinster to within 10 metres of the Scarlets line and Hickie provided the burst of pace to score, Contepomi again converting.
That score was Hickie's 24th in Celtic League rugby, bringing the Ireland wing level at the top of the all-time try list with former Newport Gwent Dragons flanker Jason Forster.
Hickie almost had the record to himself within moments as Leinster again threatened, only to spill the ball as he was tackled going for the corner flag.
An injury to Dwayne Peel disrupted the Scarlets' silky service, the scrum-half going off to ice a bang to his elbow, but Jones settled things down with his second penalty.
A fine bit of trickery from Leinster centre Luke Fitzgerald carved open the Scarlets defence to send lock Hogan under the posts for a converted try.
Although Scarlets had failed to recapture their first-half flair, they retained enough attacking threat to carve out more chances for Jones' boot.
The Wales and Lions fly-half stretched the lead to 33-21 with his third penalty, keeping Leinster at arm's length until the final whistle.
Scarlets: Ceiron Thomas; Mark Jones, Matthew Watkins, Regan King, Dafydd James; Stephen Jones, Dwayne Peel; Iestyn Thomas, Matthew Rees, Craig Dunlea, Inoke Afeaki, Scott Macleod, Simon Easterby (capt), Gavin Thomas, Alix Popham.
Replacements: Deacon Manu for Dunlea (40), Ken Owens for Rees (83), Adam Jones for Afeaki (40), James Bater for G. Thomas (78), Clive Stuart-Smith for Peel (46), Gavin Evans, Barry Davies.
Leinster: R Kearney; L Fitzgerald, K Lewis, M Berne, D Hickie; F Contepomi (capt), G Easterby; R McCormack, H Vermaas, W Green, T Hogan, O Finegan, S Keogh, K Gleeson, J Heaslip.
Replacements: R Corrigan, B Jackman for Vermaas (40), A Byrnes for Hogan (75), N Ronan for Keogh (75), C Whitaker for Easterby (23), C Warner for Fitzgerald (83), G Brown for Kearney (11).
Ref: David Changleng (SRU).