With Corus losing 22-13 at Pontyberem, Dunvant took full advantage to record a 43-16 win over Quins, with left winger Mitchell Ford and flanker Rory Gallagher each scoring two tries.
Tonmawr recorded the biggest win of the day, belting Seven Sisters 57-5 on the back of a hat-trick of tries from winger Martin Morgan. Centre Ken Morris grabbed a couple and outside-half Austin Howells kicked seven conversions and a penalty goal for a personal haul of 17 points.
Loughor and Kidwelly fought out an entertaining 27-all draw, with Loughor winger Ian Wright snatching a share of the points with a late try. Mumbles are still looking for their first win after a frustrating 21-18 loss at home to Carmarthen Athletic, but Banwen are finally on the board with a 20-16 victory at Gorseinon, who slip a couple of places in the table.
In Division 3 West, Trimsaran and Penclawdd continue their battle at the top of the table after both sides recorded big wins on Saturday.
Trimsaran fullback Thomas Bollell (four) and right winger Mark Davis (three) helped themselves to tries in a 71-12 thumping of bottom-placed Hendy, while Penclawdd ran out 47-20 winners at Pembroke Dock Quins. Tumble's impressive 30-3 win over Lampeter was their first victory of the season.
Pontarddulais have stretched their lead to five points in Division 4 West after the match between nearest rivals Neyland and Llandeilo was postponed. Pontarddulais beat Milford 34-14, with braces of tries to outside-half Jonathan Lloyd and backrower Nic Walters.
In Division 5 West, Llanybydder winger Ken Payne helped himself to a hat-trick as the leaders trounced cellar dwellers St Davids 56-0, while second-placed Burry Port beat Aberaeron 22-9 thanks to three tries from scrum-half Rhodri Morris.
Wales reached their first semi-final since 2013 in the opening round of this season's HSBC World Rugby Sevens Series in Dubai. WRU TV's Graeme Gillespie recaps on what proved to be an eventful tournament
Wales and Ospreys back row James King, who came through the North Wales age grade system, nominated North Wales Regional Community Rugby Manager Marc Roberts, in the WRU's 'Diolch' initiative where squad players thanked those who played a part in their rise to the top.
Beating Merthyr has boosted Carmarthen Quins hopes of reaching a top eight spot in the Principality Premiership. Quins captain Haydn Pugh is delighted with his team's progress and is determined that everyone from the Under 6s through to the senior team, enjoys the ride.
When the Wales squad were asked to nominate individuals who played a big part in their early playing days, Wales and Dragons full back and wing Hallam Amos thought of his former Monmouth School rugby coach John Bevan.
Sam Cross and Luke Treharne have been named as co-captains of the Wales Sevens side as head coach Gareth Williams names his 12-man squad to play in the first leg of the HSBC World Series in Dubai next weekend.
Bedwas head coach Steve Law and players Nicky Griffiths and Alun Rees extol the virtues of the close knit club as they prepare to host third place RGC 1404 - who are one place head of them on the Principality Premiership points table - on Saturday.
Many of the Wales squad have said Diolch (thank you) to someone who played an important part in their early playing days by nominating them to be invited to the Wales v South Africa match. One person, Gowerton Comprehensive geography teacher Mr Dean Mason was nominated by two of his former pupils, Dan Biggar and Sam Davies.
The second WRU disability rugby pilot has been delivered, this time in Caerphilly schools, culminating in a festival at the Caerphilly Centre of Sporting Excellence, Ystrad Mynach tomorrow. Plans are in place to set up a Disability Rugby Club in Newbridge to provide long-term playing opportunities.
WRU TV: Hear from inside the Wales camp as Neil Jenkins discusses this weekend's clash with South Africa and how the squad are looking to put in a strong performance to round of the 2016 Under Armour Series