There are six teams with six wins each under their belts and only three points separating them in the BKT United Rugby Championship table as it stands.
It means that Cardiff Rugby, on 35 points, need to build on their home win over the Lions last week when they head to Benetton Rugby in Treviso, who are five places blow them and only three points behind.
The battle for a top eight finish has never been tighter and Cardiff head coach Matt Sherratt knows there is little or no margin for error over the final five rounds of the regular season.
“We were really pleased to win last weekend against the Lions. It was an important one for us and a win which the group fully deserved,” said Sherratt.
“The league is incredibly tight this season and you can shoot up or down the table in a couple of weeks, so it is important that we continue to pick up points whenever possible. We have put ourselves in a good position, but the challenge is to stay there with some difficult fixtures coming up.
“Benetton will pose a big challenge. They have a squad full of quality and will be looking to build on a good win over Edinburgh last time out.”
Williams comes into the pack along with fellow internationals Evan Lloyd and Jim Botham. Dan Thomas goes into the back row and Ben Donnell moves up into the second row.
Another Wales Six Nations squad member, scrum half Ellis Bevan, is given a start in the No 9 jersey, with Johan Mulder dropping to the bench. Harri Millard takes over from Rey Lee-Lo at centre and Regan Grace gets his first URC start on the wing.
Ben Thomas is back on club duty after playing in every game for Wales in the Six Nations. He is one of two back line players named among the replacements.
Former Cardiff Met captain and Wales U20 cap Joe Cowell is in line for his first league appearance when he comes on in the front row.