Hooker Aaron Davies got the show on the road in the fifth minute when he scored after good lead-up work by fly half Gethin Paterson and centre Jack Davies. Jason Evans added the extras to give Abercarn an early lead.
Nick Damjanovic banged over a penalty to reduce the arrears but that was to be Trebanos's lot for the day as Abercarn asserted their authority with further tries by Jack Davies and Chris Rogers in the first spell with Evans adding a conversion and Paterson snapping over a drop goal.
Abercarn's much stronger pack provided a great platform which enabled their backs were able to play some very impressive running rugby with prop Ryan Hodges catching the eye with an impressive performance.
Flanker and man of the match Matthew Harper (converted by Jason Evans) and replacement Owen Glastonbury scored tries in the second half before centre Nicky Lloyd raced over in the right hand corner to end the Millennium Stadium victory with a flourish.
Victorious coach and outside half Gethin Paterson said: "It's been a tremendous day that the boys will treasure for the rest of their lives. It was one of the best games we've played all season, I thought our defence was great and we're a young side so this really gives us confidence for the future."
Abercarn: Tries - Aaron Davies, Jack Davies Rogers, Harper, Glastonbury, Lloyd; Cons - Evans (3); Dgl - Paterson
Trebanos: Pen - Damjanovic