Both sides were fully committed, displaying strong defensive performances in a tight first half.
It was the Scarlets who started the stronger though as they dominated the first 10 minutes. And they were rewarded with a fifth minute penalty, full-back Jack Evans slotting over a kick to give his side a 3-0 lead.
Despite their early score, it was the Blues who had the better of the rest of the first-half and they soon levelled things up for a half-time score of 3-3.
Playing with a slight wind advantage in the second-half, the Scarlets turned up the heat on their opponents, raising their level of performance significantly.
Evans extended the home side’s lead by three with a penalty in the 50th minute and although the Blues pressured the Scarlet’s line, their defence held out.
In such a tight game, the first try seemed likely to be the decider and so it proved. With five minutes remaining, the Scarlets moved the ball wide for left winger Shaun Pearce to cross in the corner.
The conversion was missed but the home side had done enough to secure the win.
In the other game, the Ospreys secured a 13-5 home win over the Dragons.
James Roberts scored the home side’s only try with James Davies and Matthew Aubrey kicking the rest of the points.
Dawid Rubasaniak’s score was all the Dragons could muster in reply.
