The Welsh region were celebrating their 5,000 match , under both their regional and previous club guise, but failed to live up to the occasion in a scrappy encounter.
 And Leinster, following a shaky start to the season in which they lost their 28-match unbeaten home record to Glasgow last weekend, took advantage to put their PRO 12 campaign back on track.
The Heineken Cup Champions led at the interval thanks to the boot of Isa Nacewa while Dan Newton slotted just the one.
Nacewa landed a third penalty just minutes after the restart but the Scarlets took the lead for the first time when Newton converted a Lee Williams try.
The Scarlets flyer crossed following the game’s best move. New Zealand Sevens star Ruki Tipuna made the initial inroads and offloaded to Aaron Shingler, who then released Williams.
Newton added the extras but Nacewa hit back with two more penalties to seal the victory .
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