The home side clinched the bonus point early in the second half before the Scarlets hit back with three tries to ensure the score had some respectability.
The home side began the stronger of the two but sterling defence by the Scarlets held the Blues at bay. Scarlets midfielder Scott Lloyd had a chance to break the deadlock but his penalty sailed wide of the uprights.
The Blues finally got some reward for their industrious work when flanker Callun James crashed over from short range. Ben Thomas’ conversion extended the lead to seven points.
The home side maintained the pressure with prop Ben Warren eventually crashing over in the corner. Thomas’ succeeded with a difficult conversion to extend the lead to 14-0.
There was time for a third try before the interval. Number eight Alun Lawrence made a break and found Ioan Davies on his inside, who was taken down. A quick ball was secured, and a stunning offload out the back by lock Joe Miles made space for Rhys Davies to slide in to give the Blues a 19-0 lead at the break.
It looked like it was going to be another long half to endure for the Scarlets when Owen Lloyd charged over after the re-start. But the Scarlets staged a fightback with impressive flanker Dan Davies deservedly crossing the whitewash to begin a second half onslaught.
Scarlets narrowed the gap further with a second try, after Ellis Thomas touched down from the back of a driving line-out.
However, the Blues secured a fifth try of the evening, with a line-out try of their own, as a move between Miles and Ieuan Morris allowed the replacement hooker to squeeze over in the corner.
The Scarlets weren’t giving in, with centre Lloyd leading the way in attack. The ball was eventually worked to Joe Roberts, who kicked behind and collected a favourable bounce to score his side’s third, but the home side saw out the final ten minutes to claim a crucial victory.
Scorers: Cardiff Blues U18: Tries: C James, B Warren, R Davies, O Lloyd, I Morris; Cons: B Thomas (3)
Scarlets U18: Tries: D Davis, E Thomas, J Roberts; Cons: S Lloyd (2)
