Wellington - The All Blacks play their final Rugby World Cup warm-up against Tonga on Saturday with coach Steve Hansen looking for a defence-busting performance from the reigning champions.

Hansen is expecting opponents in Japan to employ rush defence in a bid to smother the All Blacks' attack and derail the New Zealanders' campaign for a third straight World Cup, and fourth overall.

A hit-out against the bruising Tongans in Hamilton will give the All Blacks a chance test their attacking mettle before the tournament.

"There's definitely been a swing or bias towards defence... but someone's going to crack that nut because history tells us that will happen," Hansen said this week.

"When it does, it will open up the floodgates for the attacking game to come strong again."

Hansen, who coached New Zealand to victory in 2015 and was an assistant for the team's 2011 triumph, backed his players to succeed on attack, pointing to last month's 36-0 demolition of Australia.

However, the scope to experiment against Tonga is limited, as the All Blacks cannot afford a slow start in Japan, where they face South Africa in a blockbuster opening match on September 21.

The loser potentially faces Ireland in the quarter-finals, so Hansen wants his players to emerge from the Tonga fixture with confidence and momentum.

Hansen singled out fullback Ben Smith as a player who could benefit from a strong performance in Hamilton after struggling for form recently.

He said the 33-year-old, who is heading to French club Pau after the World Cup, needed to play his natural game.

"He's lost is his own self-belief and his confidence. Maybe that's because of injury, maybe it's because everyone's talking about him leaving and he's got caught up in that," he said.

"I want to see Bender (Smith) just being Bender. Trust his instincts, don't overthink things, just get out there and play with a big smile on his face."

Tonga, ranked 15th in the world, enter the match as underdogs after failing to beat New Zealand in five previous attempts.

"It's a massive challenge but I still believe we're a chance of playing well and getting close," coach Toutai Kefu said.

"The All Blacks are the number one team in the world, we're under no illusions about that, but we've still got a chance regardless of how small that is."

Teams:

New Zealand

15 Ben Smith, 14 Sevu Reece, 13 Anton Lienert-Brown, 12 Ryan Crotty, 11 George Bridge, 10 Beauden Barrett, 9 TJ Perenara, 8 Kieran Read (captain), 7 Matt Todd, 6 Ardie Savea, 5 Sam Whitelock, 4 Patrick Tuipulotu, 3 Nepo Laulala, 2 Codie Taylor, 1 Joe Moody

Substitutes: 16 Liam Coltman, 17 Ofa Tu'ungafasi, 18 Angus Ta'avao, 19 Scott Barrett, 20 Luke Jacobson, 21 Aaron Smith, 22 Josh Ioane, 23 Jordie Barrett

Tonga

15 David Halaifonua, 14 Cooper Vuna, 13 Mali Hingano, 12 Siale Piutau (captain), 11 Viliami Lolohea, 10 Kurt Morath, 9 Tane Takulua, 8 Ma'ama Vaipulu, 7 Fotu Lokotui, 6 Sione Kalamafoni, 5 Leva Fifita, 4 Sam Lousi, 3 Siua Halanukonuka, 2 Siua Maile, 1 Siegfried Fisi'ihoi

Substitutes: 16 Sione Anga'aelangi, 17 Vunipola Fifita, 18 Ma'afu Fia, 19 Dan Faleafa, 20 Zane Kapeli, 21 Leon Fukofuka, 22 James Faiva, 23 Afa Pakalani