Kiwis coach David Kidwell described their shock defeat to Tonga as "a blessing in disguise" and says belief in the side remains strong that they can achieve success at the Rugby League World Cup.

The upset result leaves New Zealand in line to face Fiji in their quarter-final in Wellington next Saturday and a less than desirable semi-final against Australia looms - if they are to get their campaign back on track.

After watching his side let slip a 16-2 halftime lead by conceding five second-half tries at Waikato Stadium, Kidwell was scraping for positives when he implied the loss would help the Kiwis sharpen their focus.

"I think this is a blessing in disguise for us," said Kidwell.

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"Talking to all of those guys in that shed, they still feel like they believe in what our campaign's about and with what we've done with the commitment that we've had over the last three and a half weeks.

"We're on a different path now and that's where our focus is."

The Kiwis looked strong in the opening half with wings Dallin Watene-Zelezniak, Jordan Rapana and fullback Roger Tuivasa-Sheck all scoring tries, while they absorbed three periods of sustained pressure to restrict the visitors to a lone penalty goal.

Their defence held firm early in the second-half but it all went sour when Tonga stormed back with David Fusitu'a scoring twice along with Tui Lolohea and Will Hopoate to steal a 24-16 lead with 15 minutes remaining.

The Kiwis scored again with Tuivasa-Sheck getting his second four-pointer, but the pressure cooker environment saw them commit costly errors before Fusitu'a stole a third to seal the result.

"We let ourselves down in the discipline areas that were normally very good at and then that forced us to try and play some footy and caused us to make some errors," said captain Adam Blair.

"You've got to give them credit for the pressure they put on us and if you give them a bit of football and they're a hard team to stop."