The Bridgend team were hoping to repeat their success from last season when they beat Clwb Rygbi Caerdydd at Sardis Road, while Blackwood Stars were back for the first time since winning the trophy in 2002.
Bryncethin led 9-7 at half-time after dominating the first period thanks to three Gareth Pearce penalties. He ended up with four penalties and a drop goal while Blackwood skipper Neil Cotter scored his side's first half try.
Burkby's 23 points proved the difference after the sides were level with just a quarter of an hour remaining. The outside half worked his way through to the line twice in quick succession to take his side clear and spark the Gwent celebrations at the home of Welsh rugby.
Blackwood Stars: Tries: N Cotter, M Burkby (2). Pens: Burkby (2). Cons: Burkby (2). Drop goal: Burkby
Bryncethin: Pens: G Pearce (4), A Veasley. Drop goal: Pearce