Despite the eventual result, it was Pembrokeshire who started fastest, their forwards gaining the upper hand in the early exchanges. With so much ball, a try was inevitable and wing Luke Conbeer provided the finish in the left corner.
The score seemed to shock Gower into a response and Williams soon responded with his first try of the day. Fly half and Wales U18 man Liam Popham converted as his side retook the lead.
In a see-saw encounter, both sides had chances but neither could quite stamp their authority on the game. It took a moment of magic to create the next score, a lovely pass through his legs from a Pembrokeshire player finding lock Bronzac Burley to dive over.
The conversion was missed and the home side were made to pay as Popham showed his international class. The versatile fly half, who can also play full back, dived over for a converted try of his own to give Gower a 15-10 half time lead.
And after the interval, the visitors pulled further clear as they used their big forwards to their advantage.
Ryan Jones proved fighting fit, unlike his namesake in the Wales squad, to cross for another try before Oliver Evans responded for Pembrokeshire.
But when Tom Maggs and Williams added further scores, the game was up for the west Wales outfit.
Watch highlights of today's game on S4C at 11.20pm.