But the Blues had to come from behind to take the trophy after full back James Russell had given the Scarlets the lead courtesy of two first half penalties.
Harley Thomson halved the deficit with a penalty shortly before the interval although they were fortunate to go into the break only three points adrift as the Scarlets were particularly strong in the opening 40 minutes.
George North was particularly prominent for the Scarlets with a number of strong runs in midfield, but after that, the Blues took over in control.
A charge down by scrum half Lewis Jones led to a try for Brecon's Harris and though it went unconverted, the Blues made sure of the spoils when replacement Lewis Williams kicked a late penalty.
Blues head coach Gethin Watts said; "I think it is just reward for the hard work that has gone in since they came together in June.
"There is a great deal of history in this competition with the likes of Dan Biggar and Leigh Halfpenny having played at this level in recent seasons.
"It's important that these players have a competitive environment, but it's not just about these 80 minutes today and about finals and trophies, it's about the players' development.
"The region is very proud of these players as they are vital for the future of the region."