The Virginia Park side ran in nine tries as the young Scarlets side fell to their seventh loss in eight games.
In the upset of the round, Bedwas beat a high-flying Swansea side 40-35 as the All Whites' title hopes hit their first obstacle. Home fly-half Paul Williams collected 20 points in a nine-try thriller, with Bedwas winger Nathan Hill scoring the winner in the final minute.
Cardiff's poor season continued with a 17-27 loss to Newbridge at the Arms Park, with skipper Damian Cooper getting two of the visitors' four tries.Pontypridd fell 16-27 at Carmarthen, with Quins No 8 Alun Mason bagging a brace of tries as his side push their way towards the top of the table.
Aberavon confirmed second place in the table with a 30-15 win at home to Ebbw Vale, with prolific try-scorer Lenny Woodard adding two more to his 100-plus total. Vale winger Kevin James, who played for Neath last season, scored two tries for the visitors.
Bridgend sneaked past Cross Keys 29-28 - despite four tries to Keys winger Gareth Chapman - while table leaders Newport accounted for bottom side Llandovery 54-35 in a 13-try spectacle.
Results: Aberavon 30 Ebbw Vale 15, Bedwas 40 Swansea 35, Bridgend 29 Cross Keys 28, Caerphilly 57 Llanelli 17, Cardiff 17 Newbridge 27, Carmarthen Quins 27 Pontypridd 16, Llandovery 35 Newport 54, Neath 26 Pontypool 13.