Leinster's Jonathan Sexton tackles Scarlet Josh Turnbull in Dublin
Leinster put a further dent in the Scarlets' Magners League play-off hopes with a hard-fought win in Dublin.
The hosts climbed one place to second while the visitors dropped two places to sixth, their plight also hurt by Cardiff Blues' 16-11 win at Edinburgh.
Niall Morris and Isaac Boss crossed for Leinster and Jonathan Sexton kicked their remaining points.
Rhys Thomas and Nick Reynolds touched down for the Scarlets and Rhys Priestland kicked five points.
However, Wales fly-half contender Priestland also missed 11 points with the boot - three penalties and a conversion - and also failed with a vital attempted tackle that would have halted Morris' ninth-minute try.
The Scarlets lost skipper and loose-head prop Iestyn Thomas to a neck injury in the hours leading up to kick-off.
In his absence the visitors enjoyed the greater share of territory, possession and chances in the opening quarter, but the hosts provided a lesson in profiting from the pressure they generated.
Having weathered the visitors' early attacks, Leinster built up their own head of steam and as the Scarlets' defence began to open up, Isa Nacewa put Morris into space on the right.
The wing still had a lot of work to do, but he made it look easy, wrong-footing Priestland and fending him off to cross in the ninth minute and Sexton converted.
The fly-half added a penalty 10 minutes later while Priestland missed three shots at goal before succeeding after 17 minutes.
That left the visitors trailing 10-3 at the break, having seen the good attacking work of Ben Morgan, Regan King and Gareth Maule at least giving the Scarlets belief in what they had to offer.
Analysis: Leinster 26-15 Scarlets
But with Leinster half-backs Boss and Sexton guiding their efforts and some impressive ball-carrying by back-row man Rhys Ruddock, the hosts were also able to underline their credentials.
They also had the game's outstanding performer in openside flanker Dominic Ryan, whose efforts were impressive enough for him to beat Sexton to the man-of-the-match award.
Sexton added two more penalties after the break as their momentum told on the Scarlets' defence.
And a third second-half shot from Sexton gave the hosts a 19-3 cushion with more than a quarter of the game remaining.
However, the Scarlets refused to buckle and battled back with a hard-earned try for tight-head prop Rhys Thomas.
The seven-times capped Welsh international played his part in the scrum from which number eight Morgan enhanced his ball-carrying reputation.
Morgan almost went over as he charged down the blindside, but after he was halted, Thomas arrived with half the Scarlets pack to gather and burrow over.
Priestland converted superbly from the touchline to further lift the visitors.
But their joy was short-lived. Having sat on their lead and seen it eroded by the Scarlets, the hosts responded with telling effect.
Scarlets skipper Maule was banished to the sin-bin for the dying minutes after illegally halting a Leinster attack.
The hosts opted for a close-range scrum from the penalty and after Ruddock again made ground Boss's outstretched arm brought the try and Sexton converted.
That sealed victory, although Nigel Davies' side were able to depart having conjured a try for replacement wing Nick Reynolds despite being a man down behind the scrum.
Leinster: Nacewa; Morris, O'Malley, McFadden, D Kearney; J Sexton, Boss; van der Merwe, Strauss, Wright, Cullen, Toner, McLaughlin, D Ryan, R Ruddock. Replacements: Riordan for D Kearney (71), Harris-Wright for Strauss (75), Shawe for Wright (64), Hines for Cullen (26), P Ryan for D Ryan (75). Not Used: McGrath, O'Donohoe, Madigan.
Scarlets: Newton; North, King, Maule, Ajuwa; Priestland, Knoyle; R Jones, Lawrence, R Thomas, Reed, A Shingler, McCusker, Turnbull, Morgan. Replacements: D. Evans for Newton (67), Reynolds for Ajuwa (51), G Davies for Knoyle (51), Myhill for Lawrence (64), Gardner for R Thomas (64), Welch for Reed (64), J Edwards for Turnbull (59). Not Used: P. Edwards.
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