While it wasn't the Olympic title defence they were dreaming of after their Rio gold medal, the Australians finished the tournament on a high.

The Americans put a large dent in Australia's campaign in the pool game when they came from behind to book a 14-12 win and top the group.

That put Australia on a quarter-final collision course with Fiji with their medal hopes ending by the same scoreline.

But the green and gold had the last laugh in Tokyo, and it was some youngsters who got on the scoreboard, ensuring a bright future.

Faith Nathan, 21, crossed for the opening try in the corner after a well-worked play from a scrum.

Nathan also set up 20-year-old Madison Ashby's try for Australia to take a 10-0 lead into half-time.

The United States turned up the pressure in the second half when Naya Tapper shrugged off two tackles to make a charge down the sideline before passing back inside for Kristi Kirshe to score.

Demi Hayes, 23, then chimed in with a try to secure the winning margin.

Meanwhile, the New Zealand women secured their first gold in their national sport in the second Olympics to include rugby sevens.

Tries from Michaela Blyde, Gayle Broughton, Stacey Fluhler and Tyla Nathan-Wong, who also kicked consistently, sealed their 26-12 win over France in the gold medal match.

And Fiji, whose men's team took gold for the second time on Wednesday by beating New Zealand, secured bronze with a 21-12 victory over Great Britain.

Alowesi Nakoci scored two tries for the Fijians who claimed their first Olympic medal in women's sevens.

Australian Associated Press