Canada came second, overhauling a 10-0 deficit to secure a 22-10 victory over Australia in their third game.

Leti-I'iga crossed for her first try in the opening minute and the Black Ferns went on to score six more.

The Black Ferns would have slipped outside the top two in the world rankings for the first time with a loss to the Americans but that never looked likely after scrum-half Arihiana Marino-Tauhinu crossed for the second try after six minutes.

Marino-Tauhinu, playing her eighth Test, took player of the match honours for her performance, which included a neat inside pass that set Leti-I'iga on her way to her third try in the second half.

"I think the squad has gelled really well under our new coaching administration and you can see that out on the pitch, the girls really want to keep playing regardless of the conditions," said captain Ruahei Demant.

Former All Blacks assistant coach Wayne Smith was brought in as director of rugby after a culture review led to a coaching overhaul following heavy defeats against England and France late last year.

Smith will be able to call on some more experienced players, who were rested for this series, when the Black Ferns go for a sixth World Cup title from 8 October.