Morgan Stoddart made a try-scoring return following a 15-month injury absence as the Scarlets saw off Newport Gwent Dragons in the Pro12.
The replacement wing's touchdown killed off the visitors' challenge.
Gareth Maule's controversial opening try helped the hosts to a 16-3 half-time lead.
Dan Evans went over for the visitors after the break, but Stoddart's 70th-minute score secured the home win.
Having won their opening three games only to be overpowered on home soil by the Ospreys, then lose in Treviso, the home pack had some points to prove.
The Dragons arrived at the Llanelli venue looking to exploit the perceived fragility of the home scrum.
But in last season's Wales Under-20 tight-head prop Samson Lee and erstwhile Wales captain Matthew Rees at hooker alongside veteran loose-head Phil John, the hosts proved equal to the task.
The wet conditions arguably favoured the visitors - or at least mitigated against the dangerous home backs.
However Lee's man-of-the-match performance underpinned the home effort.
Visiting fly-half Steffan Jones opened the scoring with a penalty in the 10th minute before opposite number Aled Thomas levelled soon after.
The Scarlets went ahead in unusual and controversial circumstances.
Thomas's next penalty, from wide on the right, brushed the right upright and headed towards the left post.
But whether it went through the uprights was left to television match official Gareth Simmonds to determine.
The former international referee ruled that the effort had not made it through the sticks.
But having chased hard, Maule was then rewarded by Simmonds who judged the home centre had touched down from the fly-half's shot.
Thomas converted to add salt to the wound and knocked over two more penalties before the half was up for the hosts to lead 16-3.
Dragons wing Tom Prydie brushed over a penalty midway through the second half and the hope generated by that score provided the impetus for the visitors to score their try.
Former Scarlet Dan Evans's clever grubber kick could not be secured by Scott Williams and Hughes gathered to slide over.
Prydie converted, but Dragons scrum-half Jonathan Evans fell foul of referee Nigel Owens with illegal defence from a scrum in the shadow of his side's posts.
As Evans began his spell in the sin-bin, replacement fly-half Priestland kicked the penalty.
Stoddart, making his reappearance following a 15-month recovery from a broken leg, made a real impact as the game entered its final quarter with a telling run down the left.
And, with 10 minutes left, Priestland made the most of the one-man advantage to send Stoddart on an unopposed, 20-metre run-in.
Scarlets: Liam Williams; George North, Gareth Maule, Scott Williams, Andy Fenby; Aled Thomas, Tavis Knoyle; Phil John, Matthew Rees, Samson Lee, Sione Timani, Johan Snyman, Aaron Shingler, Rob McCusker (capt), Josh Turnbull, Rob McCusker.
Replacements: Morgan Stoddart for Fenby (41), Rhys Priestland for A Thomas (65), Gareth Davies for Knoyle (65), Shaun Hopkins for John (70), Ken Owens for Rees (63), Deacon Manu for Lee (70), Richard Kelly for Snyman (53), Kieran Murphy for McCusker (57).
Dragons: Dan Evans; Adam Hughes, Pat Leach, Andy Tuilagi, Tom Prydie; Steffan Jones, Jonathan Evans; Toby Faletau, Nic Cudd, Lewis Evans (capt), Adam Jones, Ian Nimmo, Dan Way, Steve Jones, Phil Price.
Replacements: Will Harries for Leach (52), Ashley Smith for Tuilagi (52), Huw Gustafson for S Jones (41), Nathan Buck for Way (45), Jevon Groves for Cudd (53).
Not Used: Coundley, Brown, Davies.
Referee: Nigel Owens (WRU)
Assistant Referees: Ian Davies, Gwyn Morris (both WRU)
Citing Commissioner: Aurwell Morgan (WRU)
TMO: Derek Bevan (WRU)