Cardiff banished their blues after failing to reach the quarter-finals of the Heineken Cup for the first time as they blitzed Glasgow to consolidate their place in third position in the Welsh/Scottish League.
Despite having to withstand considerable pressure in the first-half against a strong wind, the blue and blacks hit back with a try on the stroke of half-time to cut their deficit to two points.
Glasgow could only muster three penalties by their outside half Graeme Kiddie with the wind at their backs and as soon as Williams skipped over for his try, which Nicky Robinson converted, the game was always in their grasp.
Three more tries flowed in the second half, from Matt Allen, Gary Powell and Francois Mounier, and Robinson added two conversions and a penalty to give the home side a much needed boost with a 29-12 victory.
For Glasgow it was only their third defeat in eight games, although things are likely to get harder for them when the Six Nations comes around and puts added pressure on their leading players.
Meanwhile, at Virginia Park, Sonny Parker took the starring role as Pontypridd continued their climb up the table with a 36-16 victory over Caerphilly.
Parker ran in two of his side's three tries. Fijian outside half Nicky Little helped himself to 21 points for the visitors.
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