Kalyn Ponga returned less than four weeks after breaking his left arm in the tournament opener, and now looms as a major threat in the World Cup final.
He and fellow Newcastle Knights player Phoenix Crossland helped lead New Zealand to a 34-10 win over Tonga in Newcastle.
The victory sends the Kiwis into the decider, where they will meet either Australia or Samoa.
Before kick-off, 29,712 spectators braved severe weather to witness a tense 65-second standoff between the teams.
After New Zealand performed the Haka, Tonga's players formed a line and held their ground as both sides stared at each other.
New Zealand captain James Fisher-Harris helped end the impasse, his eyes rolled back in a look likened to the Undertaker.
Tonga prevailed in the pre-game confrontation, but New Zealand handled the wild conditions and secured the result that mattered.