Pontypridd's title bid took a big dent with a 25-17 loss at Aberavon. Matthew Nuthall scored a brace of tries for the visitors, but the Wizards' Jamie Davies kicked 10 crucial points to become the first Premiership player to score 300 points this season.
Bridgend stay second on the table after a hard-fought 29-22 win at Bedwas, with Ravens fly-half Gareth David kicking seven goals to compliment tries to Andrew Joy and Ryan Howells.
Tries to hooker Kenneth Owens and centre Darren Simpson were enough for Carmarthen Quins to beat Ebbw Vale 20-15, while Maesteg beat Glamorgan Wanderers 12-9 in a try-less match.
Pontypool beat Llanelli 19-16 and Swansea winger Nicky Thomas scored two of the All Whites' six tries in their 38-5 win over Llandovery.
In the fourth round of the Konica Minolta Cup, Dunvant beat Penclawss 26-18 and Premiership club Cross Keys sneaked home 8-3 at Whitland.