Ulster scored two glorious tries but it wasn't enough to beat a resilient Scarlets side at Ravenhill.
The hosts fought back from an early 8-0 deficit to lead 17-15 at half-time as they looked to potentially go back to the top of the Pro12, with a pair of world class tries from Craig Gilroy and Luke Marshall.
The Ireland internationals have been on the outside of Joe Schmidt's plans for the Six Nations, but offered a timely reminder of their talents with top class finishes.
Gilroy struck first after fine work from the Ulster midfield, with a chip and chase that left the Scarlets cover in the dust.
Marshall then positioned himself on the shoulder of namesake Paul after the scrum-half's break and showed a wonderful burst of pace to beat the despairing tacklers and touch down before going out of bounds.
The officials went to the TMO but Marshall did superbly well to ground the ball before his elbow hit the turf in touch.
Unfortunately, Ulster couldn't maintain their half-time supremacy as a pair of Aled Thomas penalties gave Scarlets, who got a pair of first-half tries from full-back Michael Collins, the advantage and while Ulster got three points back through the boot of Paddy Jackson they just couldn't get their noses back in front.
The defeat is a real blow to Ulster, who saw Scarlets go above them into third place behind Leinster and leaders Connacht, however Les Kiss's side still have an eight-point lead over the play-off chasers behind.
