The Scarlets had their pride dented as Leinster, rival candidates for the PRO12 play-off spots, grabbed a bonus point in a 32-5 victory in Dublin.
The hosts scored tries through Andrew Goodman, Aaron Dundon, Jordi Murphy and John Cooney.
Andy Fenby touched down for the Llanelli side's only try, as Leinster added 21 unanswered points after the break.
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England enjoyed a winning send-off to their Australia tour as they recovered from early problems leaving Wales floundering.
Veteran singer Sir Tom, 75, is gearing up for his first concerts since wife Linda died after a "fierce" battle with cancer in April.
It will be a dry and fine day across the country with plenty of warm sunshine and light winds.