Fly half Rhys Patchell had given Cardiff Blues an early lead in the Sunday afternoon fixture, but it was departing home hero Rhys Priestland who gave the home side the comfort of a 9-3 lead at the interval.
A physical and bruising derby day battle also saw Blues count the cost of the walking wounded with Gareth Anscombe, Matthew Rees and Jarrad Hoeata all forced off in the opening half.
Patchell kicked Blues back within three points at the start of the second period to give them fresh hope.
However, a close range lineout score from Ken Owens put the hosts firmly in control and they saw out the remaining time at Parc y Scarlets to claim the points on offer.
The final derby of the season was played out in front of a crowd in excess of 10,000 and a lively start saw Patchell have a kick charged down by home flanker James Davies with the bounce almost falling kindly for Alex Cuthbert before Owens led the home charge with a barreling run.
Lloyd Williams was at his snipping best as he started a counter attack from deep with a typically direct run around the fringes while young centre Garyn Smith enjoyed a busy opening and looked to exploit gaps on the other wing.
Much focus in the early minutes was also on the set piece and in particular the titanic battle up front between powerhouse props Craig Mitchell and Phil John.
Blues, though, were dealt a blow as they looked to settle into the game with full back Anscombe forced off with injury and replaced by Smith as the back line was forced to reshuffle.
A huge hit from Filo Paulo on home scum half Aled Davies rocked Scarlets back and then the lock stole ball on the floor with a great turnover after Steffan Evans tried to break down the left wing.
Back came Blues and when scrum half Williams produced a sublime offload to Gavin Evans the penalty was secured for a dangerous tackle. Patchell duly gave Blues the lead while home full back Liam Williams was yellow carded by referee John Lacey.
The lead lasted five minutes as a penalty from the ever-reliable Priestland levelled the scores up before the fly half, who will next season line-up for Bath, added a second soon afterwards.
Scarlets mounted the pressure late in the first half with a succession of attacking lineouts and only a superb try saving tackle from Richard Smith denied Harry Robinson in the corner.
Hoeata became the latest player to leave the action while Priestland made Blues pay for straying offside with his third penalty of the afternoon for a 9-3 half-time lead.
Blues looked to respond with a penalty from Patchell eating in the lead at the start of the second half, after an initial midfield burst from Evans.
Patchell was in the thick of the action as a dropped pass from Jake Ball was hacked ball through and a foot race for the line between the visiting fly half and Scott Williams was just won by the midfield man.
Moments later, Patchell again showed his footballing skills when he kicked a stray ball into space, but this time it was Aaron Shingler who mopped up and then won the penalty as Blues went off their feet at the breakdown.
Both teams continued to try and force a try scoring opportunity with Manoa Vosawai coming on and introducing himself with a thunderous tackle on Liam Williams to send the home full back down.
A period of pressure from Blues saw Vosawai twice roll out of tackles, Turnbull and Scott Andrews offer themselves up before Lloyd Williams intelligently kicked in behind.
It looked set to pay dividends as Ball was penalised at the breakdown, but Patchell saw his kick drift wide left of the target as he now struggled with cramp in both legs.
Blues were then desperately unlucky as Patchell’s cross kick to Richard Smith took an awkward bounce to evade the winger as he looked set to exploit the wide open spaces.
It proved crucial as play swung back up the other end of the field and twice Scarlets turned down kicks at the posts to go for the corner.
They ruthlessly took the second chance as the driven lineout marched towards the try line and home hooker Owens touched down to a huge ovation to extend the lead to 16-6 in the final quarter.
Blues tried valiantly to force a way back during a free flowing last ten minutes, but it was perhaps fitting that a home penalty at the breakdown – where Scarlets had been so dominate all afternoon – should finally end the game.
Timeline:
20m Patchell p 0-3
25m Priestland p 3-3
32m Priestland p 6-3
39m Priestland p 9-3
43m Patchell p 9-6
66m Owens t Priestland c 16-6
Cardiff Blues: 15 Gareth Anscombe (R Smith 15), 14 Alex Cuthbert, 13 Garyn Smith (Isaacs 76), 12 Gavin Evans, 11 Joaquin Tuculet, 10 Rhys Patchell, 9 Lloyd Williams (Knoyle 70); 1 Thomas Davies (Hobbs 68), 2 Matthew Rees (R Williams 31), 3 Craig Mitchell (Andrews 55), 4 Jarrad Hoeata (Reed 37), 5 Filo Paulo (Vosawai 50), 6 Josh Turnbull, 7 Sam Warburton, 8 Josh Navidi
Replacements: 16 Rhys Williams, 17 Sam Hobbs, 18 Scott Andrews, 19 Lou Reed, 20 Manoa Vosawai, 21 Tavis Knoyle, 22 Tom Isaacs, 23 Richard Smith