A Steve Browning penalty was all that stood between the sides after a nail-biting opening period but the home side defied the atrocious conditions after half time to press home their superiority with four tries from second-row Stuart Williams, hooker Mark Breeze, prop Julian Page and Browning himself who also added one conversion.
The priceless result moves Cwmavon out of the relegation places while Nantymoel remain anchored to the foot of the table, still in search of their first point.
In the other games that survived the weather, Carmarthen Athletic moved into title contention after an impressive 28-10 away win at Kidwelly where outside half David Evans came away with a 13 point haul, while Gorseinon were too strong for Pontyberem, crossing for four tries in a 23-13 away victory.
Ammanford remain in pole position in Division Three after pipping rivals Amman United 19-12. The leaders were trailing 12-8 deep into the second half but had enough in the tank to snatch the result through an Alan Rees try and an Aled Parry dropped-goal.
Second placed Llanbydder lost ground as Gwylim Evans kicked four penalties for Aberystwyth in a 12-3 win while Pembroke Dock Quins recorded only their second win of the campaign, 13-11 at Newcastle Emlyn.
In Division Four leaders Hendy were held to a 17-17 draw by Pontarddulais while Morriston claimed a creditable 11-0 win over Trimsaran.
