A late penalty from Tredegar centre Greg Jones stopped the tide and saw the visitors emerge 25-18 winners.
Second placed Bedlinog were 22-15 winners at Rhydyfelin, while Mountain Ash crept past Llantrisant 10-6 in the clash between third and fourth.
Scrum-half Merion Thomas scored the game's only try for the Black and Ambers.
With Division Three East leaders Garndiffaith not playing, Pill Harriers moved level on points with the leaders after a five-try win at Nelson.
A pair of tries from Craig Lloyd, plus one each from Mark Wheeler, Louis Culverwell and Mark Thorogood saw Harriers pick up a bonus point which means they trail Garndiffaith on numbers of wins recorded.
Third place Croesyceiliog came back from 20-8 down on 50 minutes to win 28-20 at Rhymney. Matt Entwhistle conversion from his second try five minutes from the end saw the Croesyceiliog s take the lead, with a fourth try from Ieuan Wakefield earning the Cockerels a bonus point, denying Rhymney one in the process.
Llandaff remain top of Division Four East after a narrow win at Rhiwbina. The scores were locked at 13-13 with ten minutes remaining when full-back Nathan Rees kicked a penalty to give Llandaff the lead, which they refused to relinquish.
Nantyglo in second crossed ten times in a rampant 62-5 win over bottom club Pontllanfraith. There was two tries each for Richard Jones, Anthony Williams, Jamie Davies and Chris Williams for the Monmouthshire club.
The top two in Division Five East going into the afternoon, Blaenavon and Abercarn, met at the Recreation Ground, with visitors Abercarn running out 31-12 winners.
Tries from Matthew Jackson, Jack Davies, Nicky Lloyd and Jason Evans saw Abercarn pick up a bonus point, which sees them go ten points clear at the top of the table.Blaenavon's defeat sees them fall to fifth, behind Caldicot, Talywain and Oakdale, who all recorded away wins.