Earlier, Japan beat South Korea 25-22 26-24 25-21 to claim the bronze.
The USA came into the match at the Wembley Arena unbeaten in 21 matches in the calendar year, as the number one ranked team in the world, and with the loss of just two sets at the Games.
Their billing as pre-event favourites seemed justified as they blew away Brazil to take the first set in an awe-inspiring 21 minutes.
Shocked into life by their appalling start, Brazil quickly began to dominate at the net and the USA had no answer to the ability of Fernanda Rodrigues and Jaqueline Carvalho.
Brazil’s men will be looking to repeat the success of their female counterparts when they meet Russia at 13:00 BST on Sunday.