Former Wales and British & Irish Lions international Powell has had plenty of success at the home of Welsh rugby, but declared his win with Brecon as up there with anything he has achieved.
A hat-trick from full-back and man of the match Jake Crockett did the damage for Brecon as they held on despite a nervy finale.
Powell said: “I’m delighted for the boys who have put in a lot of hard work. To come through shows the character we have in the squad. I didn’t know who to hug at the end!
“It’s a special moment and right up there with anything I achieved in my playing career. We are going to enjoy tonight and celebrate on Monday with a tractor and trailer trip round the Brecon pubs!”
Brecon went to the break 15-6 in front, but they should have been further clear as they dominated with their scrum a potent weapon.
Crockett soared to the line twice and Dean Gunter kicked a penalty and conversion. Bonymaen’s points came from two Richard Cunniffe penalties.
Cunniffe started the second half as he ended the first with a penalty, but Crockett completed his treble following fine approach work from outstanding No 8 and captain Ewan Williams.
To their credit Bonymaen didn’t go away and tries from Nathan Eager and Jack Davies got them back into it.
Late on Gunter missed a penalty for Brecon and Cunniffe had a chance to win it, but he couldn’t succeed with a three-point attempt which struck the post.
Brecon hero Crockett said: “I never thought I’d play at this stadium let alone score three tries. I can take this to the grave with me.”
