American pair Misty May and Kerri Walsh continued their unbeaten streak to reach the final of the women's beach volleyball competition.
The favourites made some vital blocks to defeat compatriots Holly McPeak and Elaine Youngs 21-18 21-15.
Brazilians Shelda Bede and Adriana Behr will play the USA for the gold medal after they dominated their semi-final match against Australia.
The veterans brushed aside Natalie Cook and Nicole Sanderson 21-17 21-16.
Brazil also guaranteed themselves at least a silver medal in the men's event.
Top seeds Emanuel Rego and Ricardo Santos lost a set against Swiss duo Patrick Heuscher and Stefan Kobel but showed greater stamina to go through 21-14 19-21 15-12.
They will meet unfancied Spaniards Javier Bosma and Pablo Herrera for the title.
The European duo ousted Australians Julien Prosser and Mark Williams 21-18 21-18.
"It has been a surprise to get so far," said Herrera, who is ranked 15th.
"Being in the Olympic finals is the dream of any sportsman."
The women's final takes place on Tuesday while the men's matches take place on Wednesday.
The bronze medal matches will also be decided on those days.