Pro12 leaders Ulster maintained their 100% record and extended their lead at the top of the table to nine points with victory at second-placed Scarlets.
Andrew Trimble's try in the first half proved the difference as Ulster's Paddy Jackson and Aled Thomas of the Scarlets kicked four penalties each.
Winger Trimble pounced in the 28th minute for the breakaway touchdown.
Mark Anscombe's Ulster have now beaten all four Welsh clubs away from home in the Pro12 this season.
The Welsh club almost came away with nothing but Thomas secured a losing bonus point with the last kick of the game.
Ulster's latest success owed much to a strong scrum and it means the province have won 12 out of 12 in all competitions this season.
Minus all their Wales players, the Scarlets produced a stronger display after the break and the momentum seemed to with them as they got to within a converted try of their opponents.
But Ulster, a man down when Dan Tuohy was sin-binned for not rolling away, held firm in defence and will be in buoyant mood for the Heineken Cup trip to Northampton Saints on Friday.
In a match dominated by wet conditions chances were few and far between. Both fly-halves, Thomas and Jackson, missed early penalty attempts.
But on 10 minutes the Scarlets were caught offside from a kick and Jackson broke the deadlock with a penalty.
The Scarlets became the first side to put together some phases although it ended with Ulster scoring the only try of the game.
Centre Gareth Owen's pass was picked off by Trimble, who raced in from 70 metres to score. Jackson converted to give Ulster a 10-3 lead on 28 minutes.
There was more trouble for the Scarlets as they were penalised at a scrum right in front of the posts on their 22. Jackson made no mistake with the penalty kick to open up a 10-point lead by the interval.
It took the Ulstermen only until the third minute of the second half to extend their lead with a third penalty for Jackson. It was an especially crucial kick as Thomas badly missed a penalty attempt three minutes later.
But Thomas did make up for the miss by finding the target twice with penalties on 49 and 53 minutes to cut the visitors' lead to seven points.
The introduction of front rowers Rory Best and Tom Court turned the initiative back Ulster's way as they earned a penalty from a strong scrum, with Jackson converting his fourth penalty to restore a 10-point advantage.
Ulster had replacement lock Touhy sin-binned for a ruck offence but Thomas was wide with the subsequent penalty, although he was on target with the crucial bonus-point kick on 82 minutes.
Scarlets: Newton, K Phillips, Reynolds, Owen, Fenby, A Thomas, G Davies, John, E Phillips, Adriaanse, Snyman, Kelly, Earle, J Edwards, Murphy.
Replacements: Myhill, Hopkins, Manu, Vallejos, Price, A Davies, O Williams, Warren.
Ulster: Nelson, Trimble, Cave, L. Marshall, Gilroy, Jackson, P Marshall, Black, Herring, Afoa, Muller, McComb, Henderson, Diack, Wilson.
Replacements: Best, Court, Lutton, Tuohy, McComish, Heaney, O'Connor, Bowe.
Referee: Peter Fitzgibbon (IRFU)