Merthyr survived a late onslaught to beat Rhiwbina 29-26 and take home the Swalec Plate at the Millennium Stadium.
A brace of tries from Owen Morgan and further scores from Josh Flye, Osian Davies and Gareth Way sealed a league and cup double for the Ironmen.
Rhiwbina got off to a flying start with tries Brett Chatwin and Sion Summers, but were out-muscled by the Division 1 East champions.
Louis Millar and Chatwin scored late tries to pull the Squirrels back to within three, but Merthyr survived a late scare to take home the Plate.
Rhiwbina stormed into the lead after a well-worked try from wing Chatwin. Outside-half Josh Davies executed a pinpoint cross-kick which found Chatwin, and the Squirrels flyer was too quick for the covering Merthyr defence.
The underdogs stretched their lead after 17 minutes with another score out-wide. The Rhiwbina backs spread the ball to the right flank and Chris Fido offloaded back inside for onrushing full-back Summers to crash over - Gareth McCarthy added the extras.
The Ironmen replied just moments later through full-back Fyle.
The Merthyr forwards tried to shove there way over before releasing the backs who pushed the ball to Fyle.
The full-back dummied his way through the scrambling Rhiwbina defence and touched down to pull his side back to within seven points.
Flanker Davies then found a gap in the opposition defence to complete Merthyr's 12 point comeback.
The back-rower darted through a hole in Cardiff side's defence to score from 10 metres out, fly-half Steve Lang added the extra two points to draw his team level on half-time.
Merthyr, who are a division above their Plate rivals, took the lead after 47 minutes.
The pressure finally told when Morgan squeezed in at the corner following Luke Harwood's offload, taking the score to 17-12.
Morgan scored his second soon after, the lightning winger rounded his opposite man and dived over in the same corner.
Way then crashed over for Merthyr's fifth try to seal the win.
Millar and Chatwin scored late tries to take their team to within three points, but they couldn't get over the line for the winning score.
Christmas has come early at Glynneath rugby club, one of a number around Wales who have received an array of merchandise and equipment this December courtesy of the Welsh Rugby Union's £750,000 participation points scheme.
The WRU have been delivering on the scheme - which gives individual clubs access to up to £5,000 worth of supplies and equipment each for the 2014/2015 season - over the last two weeks and today (Friday) were received by a special guest in Glynneath, club president and pitch marker Max Boyce.
The Welsh Rugby Union has signed a new four year deal with specialist equipment supplier Rhino Rugby, which is set to benefit both the grass roots game in Wales and the national squad in equal measure.
We watch the new grass growing and being stitched together in this week's Principality Welsh Rugby Union Podcast. We speak to Millennium Stadium groundsman Lee Evans, Wales great Ieuan Evans gives an overview on the new strategy announced by head of rugby Josh Lewsey, while we also hear from Bedwas, Aberavon and Carmarthen Quins in the Principality Premiership.
Wales assistant coach Rob Howley was welcomed with open arms by the staff and players at Crymych recently when he hosted a training session in memory of former club captain and coach, Glyndwr Richards.
We hear about the WRU's annual report and some exciting new plans for schools and clubs round Wales in this week's Principality Welsh Rugby Union Podcast. WRU finance director Steve Phillips explains the money side, while head of rugby Josh Lewsey explains his new strategy for schools and clubs. We also get reaction from all round Wales.
The Welsh Rugby Union has launched a nationwide education programme, to help all involved in the game to recognise and remove' players with concussion. Wales, Racing Metro and Lions centre Jamie Roberts Wales assistant coach Rob Howley, WRU Head of Rugby Josh Lewsey and representatives of grassroots clubs in Wales who helped finalise the policy. We also hear from WRU National Medical Manager Prav Mathema, plus Llanelli and Cardiff in the Principality Premiership.
The Welsh Rugby Union has launched a nationwide education programme, to help all involved in the game to recognise and remove' players with concussion. Wales, Racing Metro and Lions centre Jamie Roberts took time out of his club commitments to raise the profile of the campaign launch held at Pontyclun Rugby Club.
The Welsh Rugby Union has launched a nationwide education programme, to help all involved in the game to recognise and remove' players with concussion. Interview with WRU National Medical Manager Prav Mathema.
This week on the Principality Premiership Podcast, WRU TV's Graeme Gillespie talks to Carmarthen Quins head coach Louie Tonkin who is aiming to close the gap on leading duo, Pontypridd and Ebbw Vale, with victory against Bridgend tomorrow.