The 26-year-old has mainly played a bit-part role in the campaign so far, but has been no less impressive both on the wing and at centre in helping the hosts run up 240 points and 36 tries in the pool stage.
Williams, who had never played on the wing before the tournament, reiterated that he would play anywhere on the park as long as he was in the team to face Argentina in the quarter-finals at Eden Park on Sunday.
"Hopefully we can still express ourselves out there, and play with the freedom that we have been playing," he told reporters. "But also we have to acknowledge that this is knockout football, that there's no tomorrow.
"You've just to find the right balance, not go into your shell and still express yourself but also recognise that it's finals football."
Williams has no experience of "finals football" at international level in union but has experienced it in his former career in Australian rugby league, which has a protracted playoff series every year.
"You've just got to tick all the right boxes, at this stage of the tournament, it's about tapering down, getting the mental part right," he said.
"Every team that faces the All Blacks raises their game and now it's the knockouts, they're going to raise it a bit more, we've got to be ready for that."
His namesake, lock Ali Williams, has experienced failed World Cup campaigns with the All Blacks in 2003 and 2007 and said preparation was a minor part of the equation in the knockout stage.
"Past learnings have given us a lot of experience and the reality is that what you do during the week is 15 percent of it and it's what you do out there on Sunday," the 30-year-old said.
"I think we are a bit more relaxed and we're relying on individuals to get themselves in the right mindset."
His fellow second rower Brad Thorn, another former rugby league player, said he was very much looking forward to locking horns with the Argentines, who finished third at the last World Cup.
"It's great," he said. "This level of footie is all about challenges, we have massive respect for Argentina -- scrum, lineout, forward play in general.
"So for me, it's a great thing to come up against a really good opponent and test yourself, that's why it's called a test match.
"I've enjoyed the last month, but for me this is what it's about," he added. "It's exciting, there's something on the line. I find it really refreshing, it's do the business or see you later."
The loss of fly-half Dan Carter to injury for the rest of tournament still hangs over the All Blacks camp but Sonny Bill Williams said the team were resolutely looking forward.
"It's really tough, a big blow, but he's out," he said. "I'm sure most of the boys would have given up their space, would taken that hit if we could.
"But what's done is done, we can't turn back time so we've just got to concentrate on positives and that's what we're doing."