Wales Under 20 skipper Steffan Hughes slid over in the first half in a scrappy encounter to give the home side a 5-0 lead at halftime.
In the second half Cherry and Whites fly-half Billy Burns converted his try before wing Aaron Warren replied with the Scarlets second try to secure victory.
Scarlets man of the match, Josh Turnbull said: “Conditions played a massive factor in the game, we didn’t play for as long as we wanted in the areas of the field that we wanted to play and spent a lot of time in their half.
Â
“We’ve always used the LV= Cup as a competition to breed younger players. I remember when I was coming through that’s where I got my chance to play some rugby.”
Â
