Williams claimed five touchdowns - one short of equalling the Lions' individual record jointly held by David Duckham and JJ Williams - while there were also scores for Ronan O'Gara (2), Mark Cueto (2), Geordan Murphy, Charlie Hodgson, Jason Robinson, Martin Corry, Neil Back, Gareth Cooper, Gordon D'Arcy and Ollie Smith.
"I tried hard, and I came off the pitch feeling pretty happy," said Williams, who has scored 24 tries in 29 games for reigning Six Nations champions Wales.
"We wanted to go out and put a marker down that we are a lot better than last weekend. A lot of the boys had a point to prove."
There were six tries in the first-half, but a further 11 after the break as Manawatu wilted amid unrelenting pressure from a Lions side that scored more tries in one game than during all seven previous tour matches together.
"They were too big, too strong and too fast in all facets of play,' conceded Manawatu coach Charlie McAlister.
"I would imagine it will be a good result for the Lions' morale, but we are just extremely grateful to have had the opportunity to put our guys up against such awesome athletes.
"This was bigger than big for our region - it has given us a massive profile with the Lions coming to play us."
Manawatu skipper Nathan Kemp added: "Maybe we were a little bit overawed in the first-half, and it sure was a tough day.
"But the Lions were awesome. They initiated swapping jerseys in the changing room afterwards, and a couple of our boys also came in with shorts and socks as well!"