|Scarlets (15) 25|
|Tries: J Davies, DTH van der Merwe 2 Cons: Shingler 2 Pens: Shingler 2|
|Leinster (0) 14|
|Tries: Nacewa, Tracy Cons: McFadden 2|
Winger DTH van der Merwe scored twice on his Scarlets debut as the early Pro 12 leaders maintained their 100% start.
The Canadian intercepted a loose pass to score from 80 metres after James Davies' try had given the home side an early lead at Parc y Scarlets.
Van der Merwe's second from close range shortly after the hour put the result beyond doubt, opening up a 25-0 lead.
But a bonus point proved beyond them, and the visitors hit back with tries from Isa Nacewa and James Tracy.
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The late scores left a bitter taste in the mouth for the home side as they looked well set to go on to score a fourth try in the final 20 minutes.
But there was plenty to savour in the preceding 60 minutes that laid the foundations for the fourth consecutive win, with Regan King pulling the creative strings and Van der Merwe again proving he needs no second invitation to score a try.
Steven Shingler's penalty opened the scoring and the home side's sparkling start was rewarded with the first try of the match inside 10 minutes.
A series of surges from the halfway line put Leinster on the back foot, and a sweeping move from right to left created a three-on-one overlap that flanker Davies converted in the corner. Shingler missed the conversion attempt.
Leinster slowly began to excerpt some pressure and the home side needed a superb try-saving tackle from Hadleigh Parkes in the right corner to push Nacewa into touch.
The visitors maintained territorial advantage and a try looked on the cards as the Scarlets defence appeared stretched.
But a long pass from Garry Ringrose lacked power, and Van der Merwe pounced to intercept.
The Canadian winger, fresh from scoring four tries at the World Cup, had the pace to score from 80 metres to mark his Scarlets debut in style. Shingler's conversion gave the home side a 15-0 half-time advantage.
Leinster lost centre Noel Reid to the sin-bin three minutes into the second half and Scarlets capitalised on their numerical advantage just before the centre's return to score their third try.
Patient probes near the Leinster tryline finally paid dividends as King, an outstanding creative force throughout, timed his pass perfectly for the on-rushing Van der Merwe to cross unopposed.
Shingler converted and then added a second penalty as the home side threatened to run away.
Leinster refused to lie down, though, and Ringrose atoned slightly for his earlier error by drawing the last man before finding Nacewa on his shoulder that gave the full-back a clear run towards the post.
McFadden converted, but the experienced winger was then guilty of a horrendous error by squandering a certain try when he dropped a straightforward pass five yards from the tryline.
The visitors continued to probe, and replacement hooker Tracy crossed from a driving line-out two minutes from time to give the score a respectability that had looked beyond them.
Scarlets head coach Wayne Pivac said: "We were trying to get that fourth try but weren't able to in the end.
"We've just go to be satisfied with four points and just keep moving on.
"We want to be in touch with the front runners and so far we've done that. It's been a good start, we've just go to keep building each week and make sure we improve in the areas we need to."
Scarlets: Aled Thomas; Hadleigh Parkes, Regan King, Gareth Owen, DTH van der Merwe; Steven Shingler, Aled Davies; Rob Evans, Kirby Myhill, Peter Edwards, George Earle, Tom Price, Aaron Shingler, James Davies, John Barclay (capt).
Replacements: Ryan Elias, Phil John, Will Taylor, Tom Phillips, Jack Condy, Rhodri Williams, Dan Jones, Tom Williams
Leinster: Isa Nacewa; Fergus McFadden, Colm O'Shea, Noel Reid, Garry Ringrose, Ross Byrne, Isaac Boss; Michael Bent, Bryan Byrne, Marty Moore; Ross Molony, Tom Denton; Dominic Ryan, Josh van der Flier, Dan Leavy.
Replacements: James Tracy, Peter Dooley, Jamie Hagan, Tadhg Beirne, Tony Ryan, Luke McGrath, Cathal Marsh, Mick McGrath.
Assistant referees: Wayne Davies, Greg Morgan (both WRU)
Citing commissioner: Arwel Morgan ( WRU)
TMO: Tim Hayes (WRU).