Fergus McFadden kicked a last-minute penalty to complete a hard-fought 16-13 victory for Leinster and deny the Scarlets a share of the spoils in Dublin.
Aiming to put themselves back in the play-off picture, the Scarlets impressed in the first half with a Dan Newton try putting them 10-3 in front at half-time.
McFadden's early second-half try got Leinster level and Newton and McFadden swapped penalties, before the Ireland international had the final say.
