Yet they had to survive a late scare when David Humphreys saw his last-gasp penalty fall just short. Ceiron Thomas established a 9-3 lead for the Scarlets after Liam Davies had been held up over the line before Andrew Trimble raced over for the game's opening try on the stroke of half-time.
Ireland pair Paddy Wallace and Trimble burst clear from deep following a momentary lapse in concentration by the home side and the wing won the foot-race for the corner by a nose.
David Humphreys used his wealth of experience to overshadow his younger opposite number Thomas as Ulster threatened to end the Scarlets' proud home record.
The Scarlets have not lost at Stradey Park in all competitions for thirteen months but that looked in serious danger when Humphreys gave Ulster the lead for the first time on fifty-two minutes and almost sent Tommy Bowe through with a pin-point cross-field kick.
The Scarlets had Scottish referee Peter Allan to thank for ruling out of what appeared to be a good try and Davies made the most of the decision, finishing after a burst from Matthew Watkins.
Llanelli Scarlets: Try: B Davies. Pens: C Thomas (4)
Ulster: Try: A Trimble. Pens: D Humphreys (2)