Centre Paul Steinmetz steered the home side to their eight victory of the season, weighing in with six penalties and a conversion.
The Scarlets’ Barry Davies and Ulster’s Adam Larkin swapped penalties in an otherwise uneventful opening but the game sparked into life when firstly second row Inoke Afeaki was sin binned for handling the ball on the ground before prop Martyn Madden joined him soon after.
However, despite being down to 13-men the visitors rallied immediately with the opening try of the game through skipper Dafydd James.
The visitors´ lead was then stretched to 13-3 with another Davies strike after 38 minutes, by which time the Welshmen were restored to full strength.
The Ulstermen rallied once more in injury time with a try by Andy Maxwell, converted by Steinmetz, that ensured the home side trailed 13-10 at the break.
Steinmetz slotted his second penaly just after the break and his third a few minutes later gave Ulster the lead for the first time in the game.
His boot stretched Ulster´s lead to 19-13 just short of the hour mark but he was off target soon after when Dafydd Jones stamp on Matt McCullough, for which he was sent off, offered him another chance to add to his tally.
However that was soon forgotten when his next attempt was successful as the game entered the last ten minutes.
Scarlets’ flyhalf Mike Hercus failed to reduce the arrears with a penalty with chances running out but there was still time for a sixth penalty from Steinmetz and an unconverted try from substitute Tyrone Howe.