The west-Wales region are now just two points behind the Cardiff Blues in ninth place, but are still in danger of not qualifying for the Heineken Cup as they are presently the lowest placed Welsh side in the league.
And they might rue not managing to score a bonus-point try tonight.
Ulster’s cause was not helped by David Pollock and Ryan Caldwell being sent to the sin-bin in the second half, although the Scarlets dominated possession and territory and were 15-3 ahead at the interval.
The home side scored first with a try after just three minutes, made by a break by Nigerian-born wing Joe Ajuwa.
He went close down the right before the ball was spread left and fellow wing Andy Fenby went over unopposed.
In an entertaining first half, the visitors did have their chances. Flanker Dan Tuohy had a try disallowed and then Ian Humphreys missed a drop-goal.
But it was the Scarlets, desperate to progress in the Magners League, who scored a second try on 20 minutes, when number eight David Lyons put scrum-half Tavis Knoyle on a 40-metre run to the line.
After that it was all Scarlets until Humphreys kicked a long-range penalty in first-half injury-time.
Ulster made their intentions known at the start of the second half, scoring a try in the first 86 seconds with Paddy Wallace crashing over after a break by Isaac Boss.
But just as the Scarlets feared a sustained Ulster comeback, Pollock was shown a yellow card for killing the ball in front of his posts, allowing Rhys Priestland to convert a penalty to give the home side a 18-8 lead.
Lions hooker Matthew Rees came on for the last half an hour to test the groin injury which has so far kept him out of Wales’ RBS Six Nations Championship campaign.
And he helped inspire his team to a try on the hour mark. It was finally scored by out-half Priestland but that was after the forwards had softened up Ulster by going through 11 phases.
After that the Scarlets were unable to create another chance and missed out on the bonus point.
Scarlets scorers: Tries: Fenby, Knoyle, Priestland. Cons: Priestland 2. Pens: Priestland 2.
Ulster scorers: Tries: Wallace. Pens: Humphreys.
SCARLETS: Newton, Ajuwa, King, J. Davies, Fenby, Priestland, Knoyle, I. Thomas, Owens, Manu, Reed, Day, Turnbull, Pugh, Lyons. Replacements: Roberts for Knoyle (75), John for I. Thomas (69), Rees for Owens (49), McCusker for Reed (66), Edwards for Pugh (70).
ULSTER: Smith, Nagusa, Cave, Wallace, Trimble, Humphreys, Boss, Court, Brady, Botha, O’Donoghue, Caldwell, Tuohy, Pollock, Henry.
Replacements: Danielli for Nagusa (50), O’Connor for Humphreys (62), Young for Court (62), Diack for O’Donoghue (65), Faloon for Pollock (65), Kyriacou for Faloon (75).
Referee: P Allen (Scotland).