Reigning world champions Larissa Franca and Juliana Silva of Brazil eased into the semi-finals after victory a 2-0 against Germany.
The South Americans looked at their very best as they romped to the first set with 11 points to spare, but they blew a big lead in the second before just holding on for a 21-10 21-19 win in 41 minutes.
Next up for the Brazilians, who have yet to drop a set at Horse Guards, is a semi-final against Jennifer Kessy and April Ross of the United States on Tuesday.
The USA team claimed a battling win over the Czech Republic with a 25-23 21-18 victory against Marketa Slukova and Kristyna Kolocova.
That brought the prospect of an all-American final a step closer, with the nation's second pair - Misty May-Treanor and Kerri Walsh - sending out the strongest signal yet that a third Olympic Games gold medal is within their grasp.
They completed a straight-sets dismissal of Italy's Marta Menegatti and Greta Cicolari to seal their place in the last four.
They will now face China's Zhang Xi and Xue Chen, who became the first team to book their place in the semis with a 21-18 21-11 win over Austria.
The Chinese pair have recovered well since losing their opening game of the tournament last weekend and looked somewhere close to their best as they outclassed sisters Doris and Stefanie Schwaiger.
Afterwards, Zhang was clear about their next target. She said: 'My goal, the one I set at the start, is for us to reach the final.'
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