Tredegar Ironsides were the team of the day in the Swalec Plate, claiming a terrific 31-8 win away at Rhymney, despite sitting a league below in Division Four East.
Jonathan Mills scored two of the away sides four tries and Ryan Hall claimed 11 points from the boot to seal a memorable win.
Risca of Division Four East put in a terrific performance to stun Croesyceiliog of Division Three East 20-15 away from home, while the students of Cardiff University pulled off another upset, beating Fairwater 17-14.
Rhydyfelin were the big scorers of the day, running home six tries on their way to a 41-0 demolition of Cilfyndd.
Mike Huckeridge claimed a try as Treherbert of Division Two East overcame a late scare to edge out Brecon 14-12, and
Tonyrefail came out in top of the all-Division Four East clash, beating Pentyrch 27-17 in a thrilling contest.
Elsewhere Mountain Ash beat Nelson 26-6, and Blaina claimed an impressive away win as they beat Division Three East rivals Abertillery Blaenau Gwent 20-8.
Abercarn pulled off the shock of the round in the Swalec Bowl, the Division Five East side beat Abergavenny of Division Two East 21-17.
Tries from Nicky Lloyd and Matthew Johnson had put Abercarn 13-12 ahead at half-time before Jack Davies put the home side 20-12 ahead. A late try from Abergavenny set up a tense finish, but the home side bravely held on to ensure a famous win.
John Mayler scored two tries as Old Penarthians gained an impressive 20-0 victory away at Canton and Ross Howells also claimed a brace as Ferndale beat Rhigos 20-8, Luke Rees claimed the other try for the Bulldogs.
Dowlais were the big scorers of the day as they ran in six tries to beat St Albans 45-3.
Crumlin put in a great performance away from home to beat Cefn Coed 34-0, while Usk also won away from home, they beat Llanhilleth 10-17.
Rhiwbina won 19-14 away at Cardiff HSOB, and Pontyclun also claimed a narrow win, beating Bridgend Sports 15-9. In the remaining game in the Swalec Bowl, Abervan failed to field a side against Newtown.
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