Having been out of the picture for the Tri-Nations defeat to Australia, Williams looked destined for few chances at the tournament.
However the 26-year-old was the surprise inclusion at inside centre - with Williams partnering Ma'a Nonu in the midfield.
And the former Toulon centre is excited to start the tournament.
"I want to take it in two arms and really give it a good crack," he said. "That's what I am aiming to do and am really excited to be playing.
"We want to start off with a good bang and I am thankful I am part of it."
Williams is expecting a full-blooded affair to kick-off the tournament, with Tonga looking to upset the hosts.
"The boys will be coming at us with that physical intensity but we give as good as we take and that's the mindset we've got to be in this week because the island boys, when they play, come with that physicality and that's what we've got to match," he added.
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