The Welsh side swept Gloucester aside as they won the ERDF Energy Cup 50-12 with Williams the catalyst for an explosive performance that contained seven tries.
Blues coach Dai Young put the pressure on the Lions selectors, who name their tour party for South Africa on Tuesday, by stating it would be difficult to leave behind a handful of his stars.
“Martyn, Gethin Jenkins, Tom Shanklin, Jamie Roberts and Leigh Halfpenny are all in the mix and they and others are going to be difficult to leave behind given the way they are playing,” said Young.
“I couldn’t have asked any more from the team than they gave me and it is a great achievement. But this isn’t just a result of the hard work of the players, it is down to the efforts of the board, the backroom staff and the fans.
“Our style is to take the game to the opposition and we really went out there and made our intentions clear.”
The Blues were 22-5 ahead at the interval and then ran in a further four tries in the second half as Gloucester, who they beat twice in the Heineken Cup Pool stages, were put to the sword.
Lions hopeful Halfpenny grabbed two tries in the opening exchanges to put the Blues on the front foot and Gloucester were chasing shadows after that. Full back Ben Blair also scored two tries as he helped himself to 25 points.
The only cloud for the Blues on an otherwise perfect day was a first minute injury to scrum half Jason Spice. The New Zealander was injured in the first attack of the game when he fractured his ulna in the right arm.
That injury is likely to rule him out of the Heineken Cup semi-final clash against Leicester Tigers at the Millennium Stadium on Sunday, 3 May.
