Newly promoted Pencoed out-scored Penclawdd three tries to nil in their 18-6 win, while Loughor, relegated from Division One last season, launched their bid to bounce straight back up with a 21-9 victory at Cwmavon.
Highly-tipped Carmarthen Athletic got their promotion bid off to a positive start returning from Gorseinon 26-13 winners following tries from scrum half Aled Thomas, centre Steve Davies, winger Chris Ham and Chris Harries.
Phil Rowe scored the only try as Pontyberem beat Nantymoel 19-0.
Aberystwyth are intent on making another strong push to join those sides after narrowly missing out on promotion from Division Three last season and began with a 19-11 win over Pembroke Docks Quins, Gwilym Evans kicking 14 points including a conversion of flanker Gareth Flynn's try.
Relegated Maesteg Quins and Seven Sisters resumed their rivalry, this time in Division Three South West, Quins winning 24-3. Tondu are expected to be among the promotion candidates this season and kicked off with a 15-0 victory at Vardre.
Tycroes celebrated promotion to Division Four with a home win over Milford Haven. Simon Cooper crossed twice in the 22-5 success.
Aberaeron opened their season in Division Five by beating Llandybie 24-18, brothers Rhodri and Iestyn Thomas joining Leighton Daniels as try scorers. And Penlan toasted the new Division Six with a thumping 60-0 victory over Nantcaredig.