Two tries each from wing Kristian Perry, centre Gareth Price and scrum-half Rhys Hallet together with scores from number eight Dean Gibb and Trevor James allowed Blackwood to canter home 54-15.
Third-placed Merthyr suffered a setback with a 41-26 defeat at Llanharan as doubles from wing Lee Thorne and centre Lloyd Thomas did the damage in the six-try victory.
Bargoed gained ground on the leaders by clinching a 30-3 bonus-point win at Rumney.
Brothers Darren and Rhys Humphries crossed while tries from Mike Roberts and Lee Pearson gained the extra point to seal a convincing victory.
Carmarthen Quins look certainties to be crowned Division One West champions after their 42-17 demolition of second-placed Narberth.
Jason Harris bagged two of the away side's five tries to put them 22 points clear at the top.
The only sour point for the runaway leaders was the red card of Martin Morgan for a striking an opponent on 63 minutes.
The result enabled Tonmawr to leap into second thanks to their 27-14 win over Carmarthen Athletic.
Nigel Francis guided the visitors with a seocnd-half try in a 17-point tally to complement tries from Gareth John and Will Price.
A Tom Brooks try handed Bonymaen a decisive 10-8 home win over fellow strugglers Cwmllynfell who grabbed a consolation score through Alan Stere.
And in the remaining game a late Ellis Phillips try helped Llangennech - in another low-scoring contest - on their way to a 10-3 victory over Maesteg.