The Valley Commandos had won six from six ahead of their trip to The Wern on Saturday but, despite holding an early lead, the derby day bragging rights belonged to The Ironmen who prevailed 28-25.
Joe Miles’ unconverted try and two Ioan Evans penalties had the visitors 11-3 ahead at the midway point in the first half, but Merthyr responded with tries from former Wales back row man Sam Cross and Jack Perkins, along with a conversion and two penalties from Ben Jones, to lead 18-11 at the break.
Flanker Perkins grabbed his second try after the re-start, again converted by Jones, who then landed his third penalty with 12 minutes remaining.
Late tries from Lucas Welsh and Cai James did at least ensure Ponty headed back down the A470 with a losing bonus point. Evans and then Jaydan Pugh added the extras to the tries.
For Merthyr, third in the table, the result closed the gap at the top to just two points and saw them return to winning ways having slipped to back-to-back league defeats by Bargoed and Llangennech.
Ponty are now just a point clear of second placed Neath, who made it six straight wins with a magnificent 46-21 bonus-point triumph over Bargoed at The Gnoll.
Lock Matthew Davies was at the double, while captain Ben Williams, wingers Nathan Orrells and Matthew Jenkins, centre Kieran Charles and flanker Gethin Tremlett also scored for the Welsh All Blacks.
Steff Williams converted four of Neath’s seven tries and kicked a penalty. Ex-Cardiff No 8 Tom Rice and wing Josh Congreve replied for Bargoed, who were also awarded a penalty try. Josh Prosser added two conversions.
Narberth climbed off the bottom after they bagged their first league win of the season at the seventh time of asking with a 29-27 triumph at Bonymaen.
Ashley Sutton, Will Blackburn, skipper Tom Powell and Ilan Phillips all dotted down for the Otters. Jonathan Rogers added three conversions and a penalty.
Wing Nathan Brooks scored twice for Bonymaen, with Gareth Andrew and Garan Williams also on the scoresheet as they took two bonus points in what was their fifth straight league defeat. Cameron Setter kicked the hosts’ other seven points.
Victory for Narberth saw them leapfrog Newcastle Emlyn, – although the latter recovered from a 26-14 half time deficit at home to Ystrad Rhondda to claim a share of the spoils from a thrilling 33-33 draw and avoid a seventh defeat on the bounce.
Reece Morris and Steffan Evans both bagged braces for Emlyn. Ellis Payne sent over two conversions and three penalties.
Cole Morgan and Cavan Davies both ran in two tries for the visitors, who were also awarded a penalty try. Rhys Truelove sent over three conversions.
Brecon, meanwhile, bagged a last play of the game 24-22 home victory over Llangennech. Rhys Williams, Matthew Williams and Lewis Jones ran in the tries for Brecon, all improved by James Dixon, who also kicked a penalty.
A fourth win of the campaign took Dale McIntosh’s side up to fifth in the table ahead of a trip to Sardis Road to face his former club Pontypridd on Saturday.
Llangennech, fresh from their stunning win over Merthyr and looking to make it five wins on the spin, ultimately had to settle for a losing bonus point after this last-gasp loss. Callum Jenkins, Shaun Edwards and Luke Davies got the Llan tries. Steff Marshall added two conversions and a penalty.
