The priceless win eased the woes at the Arms Park after they slumped to defeat in their opening two encounters this season.
To add insult to injury, former Scarlets Mike Phillips and Andy Powell grabbed vital five pointers for the home side and inspire the victory.
Phillips was first to score after only 12 minutes when he pounced on a loose ball behind the visitors’ scrum, kicked it downfield before outpacing the scrambling defence to dot down.
Nicky Robinson added the conversion to an earlier penalty to put the Blues in control of the game with the Scarlets only reward for their efforts a Mike Hercus penalty.
The woodward proved a key player in the half as four other penalty attempts, two for each side, hit the post.
The Scarlets raised their game in the second period and got immediate results.
Blues wing Craig Morgan gambled on an attempted intercept but missed, leaving Lee Byrne to benefit. He then raced clear before passing inside for half-time replacement Paul Mackey to dive over.
The Blues rallied again and a Robinson cross-kick was plamed down superbly by Morgan to Powell who grabbed the easy score.
Robinson added the extras before replacement flyhalf Gareth Bowen pulled three back for the visitors. But Robinson capped an excellent individual performance with a drop goal later in the half.
The Scarlets fought to the final whistle and forced the Blues to defend desperately in the closing quarter and flanker Robin Sowden-Taylor was yellow-carded as they attemted to hold out.
Byrne finally crossed for the Scarlets but it was not enough.