Scarlets U18s put in a battling display but were beaten 21-12 by Cardiff in their opening match of the Regional Age Grade Championship at the Arms Park.
To their credit, both sides looked to play expansive rugby in difficult conditions.
After a tight opening 40 minutes, the West Walians led 12-11 thanks to tries from wing Iolo Griffiths and second row Ollie Close, converted by fly-half Steffan Jac Jones.
But with the rain coming down heavily in the capital, Cardiff took a grip thanks to a converted try from hooker Evan Wood and a penalty from fly-half Harri Wilde.
Scarlets play their next game in the new year when they host the Dragons on Wednesday, January 4.