Scrum-half Ieuan Evans lived up to his famous name with a crucial try for Dunvant, while fullback Mark Williams chimed in with five goals.
At the other end of the table, Mumbles recorded their first win of the season with an exciting 23-20 home result against fellow strugglers Seven Sisters. Mumbles backrower Don West scored the injury-time winner.
Trimsaran "nilled" Amman United 24-0 to retain their narrow lead in Division 3 West, although unbeaten Penclawdd's hard-fought 14-0 victory at Tenby keeps them in touch at the top.
Llangefni fullback Arwel Roberts kicked 11 crucial points as his side edged Aberystwyth 21-15, with Gareth Roberts kicking five penalty goals for the visitors. Lampeter (28-9 losers at Pembroke Dock Quins) and Hendy (16-29 losers to Llanelli Wanderers) are holding up the table.
Division 3 South-West leaders Tonna moved clear at the top with a 19-13 win at Nantyffyllon, while a try double to hooker Paul Miller helped Aberavon Quins to a 21-11 win over Bryncoch that brings them into title contention.
Pontarddulais are now eight points clear in Division 4 West after a 15-7 home win over Pembroke, thanks to tries from centre Ian Mirks and scrum-half Ian Bell. Ammanford and Neyland are doing the chasing after both recorded wins on Saturday, with the latter continuing Llandybie's miserable season with a 14-0 shutout.
Morriston took advantage of Maesteg Celtic's 16-13 win over Division 4 South-West leaders Pontycymmer to move into the share of the lead with a comfortable 27-5 win over second-from-bottom Briton Ferry.
Llanybydder and Burry Port are continuing on their merry way in Division 5 West, both making it seven out of seven on Saturday. Llanybydder beat Betws 21-10, with Burry Port denying Llangwm 11-5. St Clears' 15-13 result over Furnace was their first win of the season, with Furnace now shipping 159 points in their first six matches.