But following his recent retirement from the Test arena Williams is desperate to conquer Europe.
He is set to pen a new two-year contract at the Liberty Stadium to provide at least two more chances and knows the Ospreys have to beat Saracens tonight to keep this season's Heineken Cup dream alive.
Williams, 34, said: "The Heineken Cup and World Cup were the two things left on the top of my to-do list in rugby. Obviously we fell just short at the World Cup and I've retired from Wales so the Heineken Cup is what I have to play for now.
"The contract is there and we're ready to move ahead. I see the Ospreys being very successful and I want to be part of that - the one thing I really want to achieve here is going all the way in Europe.
"But we can't look too far ahead because we know if we lose on Friday we're going home. It's a must win game for us and hopefully that will bring the best out of us - beating Saracens would be a nice early Christmas present."
The Welsh region fell to a 31-26 defeat to Mark McCall's men at Wembley last weekend and lie third in Pool Five, trailing Saracens by three points.
Williams admits the Ospreys have to up their game if they are to avenge the defeat and urged his teammates to get stuck into Sarries' stars Charlie Hodgson and Owen Farrell.
Williams added: "Saracens are a good side but we know we can play a lot better than we did at Wembley - we didn't implement what we said we needed to.
"This time we need to go out and put on a big performance, if we do that I'm pretty sure we can beat them.
"They're a big side and we need to beat them up front before we try to go wide. We also need to contain Charlie at fly-half and get on his back a bit more instead of allowing their pack to give him an armchair ride.
"Discipline in key areas and key times was an issue for us last week and the easy answer to that is not giving away soft penalties. In the Heineken Cup you can't give these three-pointers away especially when someone like Farrell is on the opposing team.
"But we came away from that match with a point and played some good rugby despite being starved of possession.
"This time we're at home and hopefully we can be a bit more consistent, I can get my hands on the ball a bit more and we can put Saracens to the sword."