Williams and fellow flanker Jonathan Thomas, locks Brent Cockbain and Robert Sidoli, centre Tom Shanklin and wing Shane Williams all breached the Italian defence, with fly-half Stephen Jones adding four conversions.
Italy's powerful pack briefly threatened to muscle control away from Wales but the Welsh front five dug in and the visitors were in a different class behind the scrum.
"I can't give our front five enough credit," Williams told BBC1.
"They were really solid and so were our lineouts. We're happy with that."
Williams, whose all-round display will have impressed Lions coach Sir Clive Woodward, admitted there was a question mark over his try on the stroke of half-time when the video referee ruled he had managed to touch the ball against the foot of the post.
"It was quite debatable but I think it just touched the post," he said.