The Fijians ran in three tries in each half, completely dominant in winning their second successive World Series tournament after beating the Americans 29-15 in last month's Cape Town final.
Earlier, the All Blacks Sevens won the play-off for third when they beat South Africa 29-7, and the New Zealand women beat France 31-0 to win the four-team women's exhibition tournament.
The United States had toppled New Zealand in the semi-finals, scoring three tries to one in setting set up their finals clash with Fiji, who had outplayed South Africa 29-7 in the first semi-final.
