Scarlets (6) 18
Pens: Priestland (6)
Dragons (3) 3
Highlights: Scarlets 18-3 Dragons
The Scarlets carried their Heineken Cup form into their flagging Magners League campaign to win their Welsh derby well.
Rhys Priestland kicked all six of his penalties for 18 points, the fly-half a late replacement for Stephen Jones whose back injury will worry Wales.
The poor Dragons, who lost returning skipper Tom Willis early on, could only reply with a James Arlidge kick.
Wales' worries increased when wing Mark Jones went off, but back-row candidate Dafydd Jones was man-of-the-match.
The game had been billed as part of a final Wales trial ahead of Sunday's squad announcement, but a poor crowd of 6,464 at Llanelli's Parc y Scarlets were disappointed by three late injury withdrawals.
Stephen Jones saw his stand-in Rhys Priestland score all 18 points
Scarlets fly-half Stephen Jones, Dragons lock Luke Charteris and scrum-half Wayne Evans all withdrew with back injuries, but all three Wales contenders are thought to be just a few days from fitness.
Evans' replacement Danny Lee conceded the first penalty for Priestland to open the scoring in the 10th minute.
Arlidge replied for the Dragons, who have seen all eight of their games this season go the way of the home side, before Priestland's second penalty in a non-descript opening.
Willis lasted less than half an hour of his comeback after a recurrence of his calf problem, and he was followed to the sidelines by impressive Scarlets lock Lou Reed.
With half-time looming Tom Riley made the best break of the half, splitting the Scarlets' midfield defence.
The centre's kick through proved too strong for wing Richard Fussell, though, as the first half fizzled out.
Priestland extended the home side's lead with his third penalty after a huge midfield hit on the impressive Fussell from Sean Lamont.
The fly-half extended the lead to 12-3 after more Dragons offside play at a ruck, before a powerful Lamont drive nearly saw Lee Williams cross in the corner.
Dragons captain Tom Willis lasted less than half an hour of his comeback
The surging Scarlets pressure proved relentless as Priestland landed his fifth penalty, before Aled Brew was sin-binned following another offence at the breakdown.
The Dragons brought on Matthew Watkins for his debut, the Wales and former Scarlets three-quarter having been kept out by a series of injuries since his summer move from Gloucester.
Replacement Scarlets hooker Ken Owens was sent to the sin bin for failing to wrap his arm around in a tackle on Jason Tovey to give the visitors some hope going into the last 10 minutes.
But in a familiar move the Dragons went offside to gift the Scarlets a penalty, Priestland making no mistake to complete his 100% record.
Scarlets and Wales wing Mark Jones then limped off to complete a worrying night for national coach Warren Gatland.
Man-of-the-match Dafydd Jones:
"We knew it would be tough, the Dragons are playing well.
"The pack went well but we weren't happy with our game, too many basic errors. Conditions were tricky and made it difficult.
"[On his Wales chances] I'm just enjoying my rugby at the moment, Martyn [Williams] is a great player and if he's fit he plays in my eyes. All I can do is play well and enjoy it."
Dragons coach Paul Turner:
"We just weren't at the races, a penalty count of 19-7, our set piece was pretty poor.
"We missed Luke [Charteris], Tom [Willis] went off early, Joe Bearman... but at the end of day we were just not there and were second best in every department.
"The Scarlets got the momentum and six penalties to one was probably just desserts for them.
"We were pretty up for it [beforehand], injuries didn't help, but they give other players an opportunity and I'm pretty disappointed."
Scarlets: Evans, Williams, Lamont, Higgitt, M. Jones, M. Jones, Priestland, Roberts, I. Thomas, Rees, Manu, Reed, Day, Easterby, D. Jones, Lyons.
Replacements: Maule for Williams (76), Knoyle for Roberts (76), John for I. Thomas (69), Owen for Rees (57), Cooper for Reed (36), Pugh for Easterby (69). Not Used: Newton.
Dragons: M. Thomas, Brew, Riley, Smith, Fussell, Arlidge, Lee, Gustafson, Willis, Bracken, Sidoli, A.Jones, Lydiate, G. Thomas, MacDonald.
Replacements: Watkins for Smith (67), Tovey for Arlidge (64), Walker for Lee (71), S. Jones for Willis (20), Robinson for Bracken (73), L. Evans for MacDonald (71). Not Used: Charteris, W. Evans, Harris.
Referee: Peter Allan (SRU)