The Brazilians dominated at the net and committed very few errors in their 21-17 21-16 semi-final victory over 2000 Olympic champion Natalie Cook of Australia and her new team mate Nicole Sanderson.
In a battle of the Americans, May and Walsh kept up a steady defense and Walsh made some key blocks to beat compatriots Elaine Youngs and Holly McPeak 21-18 21-15 and guarantee the first women's Olympic medal for the United States.
Brazil veterans reach semis
May and Walsh have dominated women's volleyball over the past few years but Bede and Behar took the silver medal in the Sydney Games.
Top 5 beach volleyball moments at the Olympics
Where has the crowd gone?