A personal contribution of 19 points from Wales outside-half Stephen Jones helped the Scarlets to a 29-24 Magners League victory over their Welsh rivals at Parc y Scarlets.
But the Scarlets had to mount a comeback as the Dragons, who earned a losing bonus point, led at half-time thanks to two tries from Richard Fussell and then rallied at the end.
The Scarlets welcomed back Jones and Matthew Rees, as well as regional captain Simon Easterby, who were all rested for the 20-6 defeat at the Ospreys.
The Dragons handed a debut to former Nottingham prop Nigel Hall. But they were without injured trio Luke Charteris, Joe Bearman and Rhodri Gomer-Davies.
There was only one side in it in the opening exchanges as the Scarlets breezed into a 10-0 lead after nine minutes as they produced some of their best rugby of the season.
First Regan King showed his class by rounding two tackles to go over on seven minutes for a converted try before Stephen Jones planted a penalty goal after scrum-half Martin Roberts had been high-tackled.
A second try looked on the cards on 12 minutes but Jonathan Davies knocked on Mark Jones' kick ahead into the Dragons' 22.
But against the run of play the Dragons scored two converted tries through Fussell in the space of 11 minutes to take a 17-10 lead into the break.
First Fussell slid in at the left corner after Shaun Connor had set his backline going with a long pass, and he was over in the same corner again after good work by Jamie Ringer.
Colin Charvis and Rhys Thomas both went close to scoring tries before Connor made it 17 unanswered points for the Dragons with a penalty in the final minute of the half.
But he missed a relatively easy penalty in the second minute after the break which would have given the dragons a 10-point cushion.
After that the Scarlets began a concerted comeback, which was started with a Stephen Jones penalty and continued with a try for prop Phil John just before the hour mark as the home side went into a 20-17 lead.
That advantage was extended with three more Jones penalties on 60, 64 and 68 minutes
But just when the Scarlets thought they had the match in the bag Connor converted his own try to cut the lead to 29-24.
But the Scarlets held on in the last six minutes to secure the victory.
The Ospreys beat Cardiff Blues 16-12 at Cardiff Arms Park.
As head coach Stuart Lancaster polishes the axe he will soon wield over his World Cup training squad, Exeter Chiefs coach Rob Baxter has backed Jack Nowell, Henry Slade and Luke Cowan-Dickie to be given a stay of execution.
Italy Under-20s held off a late Samoa blitz to retain their place in the World Rugby U20 Championship on Saturday and head coach Alessandro Troncon believes the experience will have served as a valuable lesson for his young troops.