The defensive unit, in which Brooke Neal and Emily Gaddum produced standout turns yesterday, did a good job of protecting goalkeeper Sally Rutherford until the latter stages.
The midfield was well organized by Sam Charlton, Pippa Hayward and Kayla Whitelock, while the pace and skill of Stacey Michelsen and Anita Punt troubled Japan, particularly down the right flank.
Unlike their thrilling semifinal win over world No 3 Australia 24 hours earlier, when they surrendered an early 2-0 lead, New Zealand began positively tonight and were two goals up before the end of the first quarter.
Olivia Merry scored her fourth goal of the tournament in the third minute after sloppy Japanese defence presented her with an opening from close range.
Four minutes later, Gemma Flynn was set up by Whitelock, then beat a defender and finished her chance expertly, with fiancé Richie McCaw looking on.
Whitelock got the third goal two minutes after halftime, neatly deflecting a ball into the goal after persistence from Rose Keddell and a smart pass from Charlton provided the leadup.
However Japan were scrapping hard and had their best period to that point, Rutherford called on to stop Motomi Kawamura.
Japan, desperate to get something from the match, pressed hard in the fourth quarter and Nagakawa's two goals were good reward for them.
''It does mean a lot to us and gives us a lot of confidence going forward," Charlton said tonight.
''It's the first tournament we've won in a long time. To come away for six games unbeaten and win at home is something that's really special for us."
In the other final-day matches, Australia beat China 3-1 to finish third; Ireland won a shootout against India 4-3, after the teams finished 1-1 after regulation time to take fifth while Korea's 3-1 win over Canada earned them seventh place.
New Zealand next head to Darwin for a four-nation tournament with Australia, India and Japan late next month before travelling to London for the Champions Trophy in mid-June.
