Ruby Tui and Tyla Nathan-Wong scored first half tries to give the New Zealand a 14-0 half time lead.
In the second half, solid Australian defence stalled The Black Ferns Sevens' momentum before Portia Woodman came flying in off the left wing.
Two signature side steps and express pace left tacklers floundering in her wake as the game's leading try scorer crossed for try number 135.
19-year old Alena Saili put the result beyond doubt with a try down the left wing before Australia crossed for a late consolation.
