The first and second halves where like night and day, with Ulster edging an opening half 9-3 but then cutting loose in the second half with five tries and that all-important bonus point. Ruan Pienaar kicked superbly all evening to contribute 16 points, with tries by Robbie Diack, Nick Williams, Andrew Trimble, Neil McComb and a penalty try doing the damage in the second half.
The visitors nudged ahead in the eighth minute when Thomas stroked over a straight-forward penalty.
A sluggish and error-prone Ulster should have had been punished further but Thomas kicked an easy effort just right of the posts.
The game finally burst into life after Pienaar floated over an equalising penalty for Ulster in the 21st minute, with both teams looking to attack from loose play only for handling errors to stop any momentum.
But the momentum began to sway Ulster’s way and they twice almost crossed the line before a typical burst around a ruck by Nick Williams allowed Pienaar to squeeze Ulster ahead in the 33rd minute. A third penalty by the Springbok scrum-half on the run-up to half-time gave Ulster a lead which they just about deserved at the break.
Within two minutes of the restart Ulster had run in the first try of the evening. Hooker Rob Herring made the break in midfield and gave the scoring pass to Diack, who ran under the posts for Pienaar to convert.
Pienaar added a fourth penalty six minutes later with Ulster registering 16 points in as many minutes to take a firm grip on the game.
With Ulster now very much in the ascendancy, it was only a matter of time before try number two came along and it was through their wrecking ball number eight Williams who proved unstoppable as he took a tap penalty from five metres out. Pienaar kept his accuracy with the boot to add the extras.
The loss of their Welsh star George North, who was stretchered off in the 65th minute, didn’t stop Scarlets collecting their first try, as Josh Turnbull cut through a lazy defence to score. Thomas added the conversion.
Ulster responded with the best move of the game, with Craig Gilroy and Darren Cave involved in slick passing, and the speeding Trimble the recipient of a sumptuous inside pass to thunder in at the post with Cave drop-goaling the conversion.
Ulster wrapped up the five-pointer when the referee had no option but to award a penalty try when a back-pedalling Aled Thomas prevented a certain try on the right wing. Replacement lock McComb dived over to wrap up a useful warm-up for Europe, although Scarlets had the last word with Scott Williams diving over for their second try.
Ulster scorers: Tries: Diack, Williams, Trimble, Penalty, McComb. Cons: Pienaar 2, Cave, Jackson 2. Pens: Pienaar 4.
ULSTER: D’Arcy, Trimble, Cave, L. Marshall, Gilroy, Jackson, Pienaar, Court, Herring, Macklin, Stevenson, Tuohy, Diack, Henry, Williams.
Replacements: Andrew for D’Arcy (14), Wallace for L. Marshall (41), Heaney for Pienaar (69), Black for Court (72), Annett for Herring (72), Afoa for Macklin (41), McComb for Tuohy (36), Wilson for Williams (58).
Scarlets scorers: Tries: Turnbull, S. Williams. Cons: A. Thomas. Pens: A. Thomas.
SCARLETS: Newton, North, Maule, J. Davies, K. Phillips, A. Thomas, Knoyle, John, E. Phillips, Adriaanse, Timani, Kelly, Turnbull, J. Edwards, McCusker.
Replacements: S. Williams for North (64), G. Davies for Knoyle (61), R. Jones for John (64), Myhill for E. Phillips (69), Manu for Adriaanse (54), Vallejos for Timani (54), Price for J. Edwards (27).
Referee: Leighton Hodges (RFU).