"The result puts us in a great position now with a couple of days off before a really tough match against the Aussies."
The Black Sticks were first to score in the 18th minute when Jared Panchia picked up a deflected penalty corner drag flick from Kane Russell and hit back past the keeper.
Just out from halftime Nic Woods doubled his side's advantage, ripping a powerful flick into the side of the net from another penalty corner.
The Black Sticks opened a 3-0 buffer midway through the third quarter after Hugo Inglis found Stephen Jenness wide open at the top of the circle for a venomous forehand shot into goal.
Japan scored a consolation goal in the 59th minute when Hirotaka Zendana managed to beat the New Zealand circle defence.