Though victory was deserved with a 4-1 try-count, neither side played to expectations and it was not a good showpiece for the Division with both sides and the referee making far too many errors.
Fly half Chris Anderson, a former Neath player, opened the scoring with a penalty, but Neath hit back with a brace of tries by wing Richard Johnston, of which James Hook converted the second.
Two more Anderson penalties followed, but both he and Hook failed with attempts until Hook succeeded on the hour for a 15-9 lead. Neath skipper Gareth Morris then scored a try that Hook converted, but Cardiff replied with a dubious score from Chris Czekaj.
Another Hook penalty was followed by a corner try from Neath centre Andrew Bishop in the closing minutes.
Nearly 40 players were involved in the first Wales Under 18 training session of the season. WRU National Performance Manager Gethin Watts is excited at the potential shown by the group and expects the Regional Under 18 Championship to hone their skills even further.