Luke Marshall marked his return to the side with a try
Ulster dropped to fourth in the Guinness Pro12 standings this afternoon as the Scarlets pipped them at the post with a one-point victory which elevates the Welsh outfit to third in the run-in for a top-four finish.
Sublime tries from Craig Gilroy and Luke Marshall notwithstanding, Ulster failed to properly click into gear at KIngspan Stadium, and will rue the defensive frailties which allowed Scarlets full-back Michael Collins in for two simple first-half tries, and a lack of penetration which saw them fail to convert ample possession time in the opposing '22'.
With Rory Best unavailable through international commitments and Rob Herring nursing a hamstring injury, Paddy Jackson skippered his province for the first time and John Andrew got his first full cap at hooker.
There was also a huge personal milestone for Number Eight Roger Wilson, who collected his 200th Ulster cap to join Andrew Trimble as only the second current player to reach the double-century of appearances for the side.
Lining up alongside Jackson in the backs were Stuart Olding at full-back, Gilroy and Jacob Stockdale on the wings, Darren Cave and Marshall - released from international duty - in the centre, and Paul Marshall at scrum-half.
Andrew Warwick and Ricky Lutton propped either side of Andrew in a new-look front row, with the now-established partnership of Alan O'Connor and Franco van der Merwe in the second row, while Wilson was joined at the back of the scrum by Robbie Diack and Chris Henry, making his first start since sustaining a shoulder injury in December.
An early four-versus-one out wide on the Scarlets left after a missed tackle from Cave gave Collins the most elementary of tries on four minutes, but an intentional knock-on from the visitors gifted Ulster a close range lineout which promised much, but delivered nothing as Paul Marshall fumbled forward as he fished out of the back of the maul.
Another missed tackle in the wide channel - this time from Olding - gave the Scarlets licence to roam in the Ulster '22' where an eventual infringement in front of the posts saw out-half Aled Thomas kick over his penalty for an eight-point lead on 15 minutes.
Jackson's drop-goal with an Ulster penalty imminent reduced the gap immediately, and with the hosts now seemingly roused from their Sunday afternoon siesta, the next Scarlets attack was efficiently snuffed out in double-quick time before Gilroy collected his own kick over the top to run in yet another fine individual try, converted by Jackson.
However the see-saw rhythm of the match continued, with Collins again capitalising on some patchy Ulster defending out wide to ground by the flag in a carbon copy of his first score on 24 minutes, Thomas this time adding the conversion.
Ulster contrived to waste a fortuitous lineout steal on the half-hour, lacking penetration as forward after forward attempted in vain to pile over from five metres until the Scarlets wrestled back possession, but much better from the backs saw a trademark dart from Mr Nippy Paul Marshall create the space for his namesake Luke to touch down just within the limit of the right-flank touchline, the centre displaying superb upper body strength to fend off two tacklers as he stooped to ground.
Jackson added the conversion, and Ulster had good fortune to thank as Thomas struck a simple penalty against the upright just on the stroke of half-time to enable them to run off with a slender lead.
Half-Time Score Ulster 17 Scarlets 15
Scarlets stormed into the second half in voracious mood, pounding the Ulster line straight from the off and eventually earning the penalty which Thomas dispatched on 46 minutes to re-establish their lead.
Worse still for Ulster saw Henry sin-binned on 49 minutes for illegal handling and Thomas extend the gap to six, but the hosts did well to retain the ball for virtually the entirety of their flanker's exile, and when Henry regained the field on the hour-mark along with multiple replacements including Ruan Pienaar, Ulster points were not long in coming - Jackson slotting home a 63rd-minute penalty.
A single point adrift, Pienaar kicked a subsequent penalty to touch, but despite setting up camp in the Scarlets '22' for a good 10 minutes, the Ulster breakthrough refused to come and the Welsh cleared their lines on 73 minutes.
Deep in their own '22' with four minutes left to play was not where Ulster wanted to be, and it was game over when referee Ian Davies awarded a penalty to allow the Scarlets to play keep-ball in the corner.
Full-Time Score Ulster 20 Scarlets 21
Ulster (15 - 9) Stuart Olding; Craig Gilroy, Darren Cave, Luke Marshall, Jacob Stockdale; Paddy Jackson (c), Paul Marshall
(1 - 8) Andrew Warwick, John Andrew, Ricky Lutton, Alan O'Connor, Franco van der Merwe, Robbie Diack, Chris Henry, Roger Wilson
Replacements (16 - 23) Johnny Murphy, Kyle McCall, Bronson Ross, Peter Browne, Clive Ross, Ruan Pienaar, Ian Humphreys, Sam Arnold
Scarlets (15 - 9) Michael Collins; Gareth Owen, Regan King, Hadleigh Parkes (c), DTH van der Merwe; Aled Thomas, Aled Davies
(1 - 8) Phil John, Kirby Myhill, Peter Edwards, George Earle, David Bulbring, Aaron Shingler, Will Boyd, Morgan Allen
Replacements (16 - 23) Ryan Elias, Dylan Evans, Rhodri Jones, Maselino Paulino, Rory Pitman, Rhodri Williams, Dan Jones, Steffan Evans