Second-row Sam Williams scored twice as Llantrisant ran in seven tries to take an early grip on the division ahead of their rivals.
Tredegar slipped to third after losing 31-24 to local rivals Brynmawr for whom flanker Gavin Napp scored twice while at the other end of the table, Fleur de Lys claimed their first win when Richard Jones' late try beat Rhydyfelin locked at 25-18.
Llanishen enjoyed themselves in the sun with a 52-6 win over Cardiff rivals Old Illtydians in Division Three south-east
while Treorchy gained another bonus-point win at Aberdare, 35-20.
Gwernyfed and Garndiffaith lead the way in Division Three after their victories, 29-7 at New Tredegar and 29-15 at Cwmbran respectively.
Barry Greenley, Paul Rees, Chris Voyce, Stuart Ornick and Nathan Rhys all scored as Llandaff lowered the colours of Division Four leaders Nantyglo, 29-21 in Cardiff to take over top spot themselves.
In Division Four south-west, Dowlais had little trouble dispatching Porth 48-12 while Jack Davies and Gavin Stokes both scored twice as Abercarn produced the performance of the day in Division Five East, beating Llanhilleth 37-7.
Barry scrapped out a second tight victory in a row, getting the better of Cilfynydd 12-7 in Division Five south-east.