Blues outside half Gareth Thompson traded penalties with Dragons opposite number Ethan Davies before the impressive full back Hallam Amos hit the line like a bullet to speed over from 35m to give the Dragons an 8-3 lead.
The Blues regained the lead on the stroke of halftime after a period of sustained pressure. Joe Raikes kicked the ball deep into the heart of Dragons territory and with the defence in disarray, referee Ben Whitehouse adjudged Ollie Smyth had been tackled without the ball and awarded a penalty try. With Thompson adding the conversion, the Blues went in at the break 10-8 ahead.
The Dragons refused to buckle and edged back in front in the 55th minute with a Davies penalty before the power of the Blues pack made their presence felt again.
From a driving line-out, Ben Roach powered his way over for a well worked try to put the Blues 15-10 in front. Thompson then had a chance to put the game beyond the Dragons reach but he missed a relatively straight forward penalty.
This spurred the Dragons on and they threw everything at the Blues but they couldn't find a way through.
For the victors, Roach, along with Ethan and Callum Lewis were outstanding in the contact area for the Blues, while Amos was a constant threat whenever he was near the ball for the Dragons.
Blues Under 18 team manager Iestyn Williams, said: "I'm delighted by the result. The win is a fantastic reward for the players and the coaches. It's a remarkable record as this is the third time in three years that the title has gone back to the Blues."