It was tough, hard, but never dirty and both clubs gave it their all, but Mountain Ash looked smart in their kit and played just as smart as Merthyr dropped too many passes behind the scrum.
If there was a hero for 'The Old Firm', as The Mount are often called, then it was two-try left wing Dean Phillips. Right on time he almost caught a high ball for his hat-trick, but the cheers that rang out were instead for the final whistle blown by referee Sean Brickell, whose late grandfather Alfie had played for Wales against England in a 1946 Victory International.
Merthyr had to play catch-up and despite some huge kicking by Neil Burnett, they never quite made it against a disciplined Mount pack that hooker Craig Evans led outstandingly.
Two young fly-halves Tom Pascoe and Josh Lewis were well served by scrum-halves Meirion Thomas and Jonathan Hooper, but the Pascoe-Thomas partnership had better ball to play with.
The aptly-named lock Craig Lock, who has been signed by Pontypridd, was a big man in the Mountain Ash pack and No8 Chris Edmunds also excelled.
Merthyr had their moments of pressure with centre Adam Williams making the breaks, but it was always to be The Old Firm's night.
After Burnett had kicked a penalty and Pascoe dropped a goal, scrum-half Thomas went blind, drew his man and sent wing Phillips racing over in the corner for an 8-3 lead.
Burnett pulled back a penalty, then missed by inches from well inside his own half.
Pascoe calmed nerves with a penalty and just on the interval came the moment of the match as skipper Evans unloaded to Thomas, who went right, but turned the ball back left and wing Phillips was free and racing over for Pascoe to convert at 18-6.
It seemed as if Merthyr must come back and, indeed, replacement hooker, New Zealander Troy Brockbank, burst over for Burnett to convert and after 53 minutes Burnett's penalty narrowed the gap to three points.
But it was the Mount's night and though Pascoe narrowly missed twice, he goaled a 61st-minute penalty that extended the gap to six points.
However, it was not a case of hold on as Merthyr spilt too much ball and no further score came to either side.
The winners were presented with the cup by Martin Anderson, regional director of Molson Coors and wing Phillips was named man of the match.
Mountain Ash: Gavin Roberts; Ethan Davies, Dale Keepin, Craig Roberts, Dean Phillips; Tom Pascoe, Meirion Thomas; Gavin Powell, Craig Evans (capt), Craig Thomas, Craig Lock, Jonathan Lewis, Kriss Saunders, Chris Edmunds, Scott Davies
Replacements: Geraint Lock, Dean O'Brien, Richard Griffiths, Gareth Waters, Matthew Parfitt, Nigel Roberts, Jonathan Lock
Tries: Dean Phillips 2 Con: Tom Pascoe Pens: Tom Pascoe 2 DG: Tom Pascoe
Merthyr: Neil Burnett; Chris Weightman, Bleddyn Rees, Adam Williams, James Wood; Josh Lewis, Jonathan Hooper; James Howe, Robert Evans, Rhys James, Sam Wahdam, Darren Lynch, Rhys Miles (capt), Phil Rees, Matthew Rees
Replacements: Darryl Jenkins, Jonathan Watkins, Troy Brockbank, Malachy Mullins, Gareth Davies, Lloyd Hynes, James Bull
Try: Troy Brockbank Con: Neil Burnett Pens: Neil Burnett 3
Referee: Sean Brickell (Abertillery)