Sean Fitzpatrick believes the impact of Sonny Bill Williams from the bench could be the key to the All Blacks successfully defending their Rugby World Cup crown.
Steve Hansen's side were given a tough time by Argentina at Wembley on Sunday before coming from 16-12 down in the second half to win 26-16.
The introduction of Williams in the 46th minute in place of an under-par Ma'a Nonu gave the All Blacks some much-needed spark and despite playing less than half a game the former NRL star already tops the tournament offloads chart with five.
"What really pleased me was the bench," Fitzpatrick told AAP at a Laureus-supported active communications event in London.
"They wanted to give Sonny Bill a run and although he hasn't played very much rugby he came on and had 35 fantastic minutes and was probably the player of the day.
"He pretty much changed the shape of the game."
Williams' performance has led to speculation he may take Nonu's place in the side but Fitzpatrick believes the Hurricanes star has enough credit in the bank to keep his spot.
"Ma'a Nonu is the incumbent and rightly so," he said.
"He is the best 12 in world rugby ... world class.
"It's a 23-man game now and they are all going to have an input. That is the difference between the All Blacks and the other teams, they have players who can come on and make a difference.
"Sonny Bill came and made a difference, Beauden Barrett came on at 15 and made a difference.
"They have multiple ways of playing and that is what you need for different opponents."
The former All Blacks skipper and veteran of three World Cups, believes Argentina provided the best possible test and was pleased with what he saw from Hansen's side.
"I thought New Zealand played well but Argentina were quite outstanding for the first 60 minutes," Fitzpatrick said.
"But in addition to Sonny Bill, Wyatt Crockett and Charlie Faumuina came on and were also outstanding in terms of the ball carrying.
"I think in this World Cup you need 15 ball carriers and that is something the All Blacks have got unlike many other teams.
"I liked their composure. Not many teams could have lived with the Argentines in terms of the way they were playing and come out with a good result.
"They now have three games where they just need to keep their shape. They have to do a lot of work off the field in terms of physical presence and can look forward to the quarter-final."