That result was compounded by a surprise first defeat of the season for title rivals Rumney at Llantwit Fardre. Outside-half Michael Thomas was the hero for Fardre with a 21-point haul while Andrew Webb, Jonathan Hughes and Aiden Evans all went over in the 36-30 win that left Llantrisant clear at the top.
Mountain Ash lightened their relegation fears with a crucial 19-18 win over fellow strugglers Abergavenny. Gavin Roberts and Adrian Owens scoring the vital tries to lift their side above their opponents.
Chris Phew scored 23 points, including two tries, as Tredegar demolished visiting Treherbert 38-3.
Penallta wrestled control of Division Three after an emphatic victory in the top of the table clash against Newport HSOB.
Shaun Powell crossed twice while Chris Alleys, Carl Rhys, Craig Morris and Gareth Davies, who converted all five tries, also went over to take Penallta three points clear.
Brynmawr pulled off a shock 8-5 win over fourth-placed Brynithel while neighbours Blaina hit the half-century at Pontllanfriath.
Pencoed and Llanishen maintained their unbeaten starts in Division Three (South-East) with victories at Gilfach Goch and Treorchy respectively while Pentyrch lifted themselves out of the bottom four with a 17-10 win at fellow strugglers Hirwaun.
Darren Herbst bagged all the points as Machen fought out an 18-18 stalemate with visiting Llandaff North in Division Four. Monmouth took advantage of Garndifaith's cup tie to move level at the top of the table with a 36-10 win over Trinant.