A penalty by fly half Julian Huntley put Cambrian ahead and it was a lead they never lost as Huntley followed with a try that he also converted.
Bryncethin fought hard to get back on terms with hooker Neil Hopkins crossing for a try and then scrum half Lloyd Jenkins kicked a penalty to make it 10-8 at the interval.
All the scoring in the second half belonged to Cambrian with wing Gavin Thomas going over for a try that Huntley converted and then Huntley stepped up to seal the win with a penalty in a faultless performance.
Man of the match award went to Cambrian flanker and player/coach Chris Davies, but the two clubs now have two more battles to come in Division Six Central starting with the game at the Welfare's ground on Wednesday, April 23rd and the return at Bryncethin seven days later.
Bryncethin: Mike Richards; Richard Handly, Chris Williams, Jamie Davies (Capt), Russell Johns; Andrew Veasey, Lloyd Jenkins; Huw King, Neil Hopkins, Steve Walters, Jimmy Smith, Kevin Baldwin, Mark Thomas, Paul Evans, Andrew Bayliss. Reps: Gareth Pearce, Rowan Hobbs, Rhys James, David Bayliss, Leighton Jenkins, Peter Puaca, Tony Stevens
Cambrian Welfare: Phillip Gowans; Jonathan Richardson, Paul Martin, Christian Ashford,.Gavin Thomas; Julian Huntley, Jonathan Jones; Lee Thomas, Mark Whitford, Craig Griffiths, Damon Filmer, Kevin Lawrence, Chris Davies, Robert Norton, Anthony Jones (capt). Reps: Craig Chedzoy, Zak James, Craig Meredith, Ritchie Lewis, Matthew Jones, Mark Jones, Wayne Morgan
Referee: Kelvin Shorte (Cardiff & Dist RU)