Britain's Steve Grotowski and John Garcia-Thompson suffered a second straight defeat but not before putting on a valiant performance.
The pairing of Ricardo Santos and Pedro Cunha simply had too much power and experience for the British duo in their Pool F match.
The customary boisterous crowd at the 15,000-seater arena inevitably did their bit to help the British players, but the Brazilians nevertheless wrapped up a 21-17 21-12 win that sees them through to the knockout stage.
Latvia's Aleksandrs Samoilovs and Ruslans Sorokins also powered into the knockout phase with a straight-sets dismissal of South Africa while there were also wins for Norway, Poland and Switzerland.
In the women's, the highlight of the day saw defending two-time Olympic champions Misty May-Treanor and Kerri Walsh maintain their stunning record at the Games with a straight sets win over the Czech Republic.
May-Treanor, celebrating her 35th birthday, bossed the opening set with a series of winning attacks at the net to set the United States duo on course for a win that takes them into the knockout stage.
Elsewhere, China beat Switzerland 2-1 and Brazil beat Germany 2-0 in the other standout results.