Reigning two-time women's champions Misty May-Treanor and Kerri Walsh dropped their first set in Olympic Games competition but fought back impressively to claim victory over Austria.
The loss of the pair's unblemished Olympic record was a huge surprise, coming as it did against sister pairing of Doris and Stefanie Schwaiger, but their response was befitting of champions and they end their Pool C campaign top of the table.
The USA looked out of sorts from the outset and were soon trailing 7-1 as the Austrians strung together some inspired passages of play.
The Europeans duly wrapped up the first set with room to spare, but that only served to bring the best out of the champions, who beat the sisters in the second before wrapping up the win in the decider.
Earlier in the day, world champions Juliana Silva and Larissa Franca of Brazil had maintained their 100 per cent start at Horse Guards Parade with victory over the Czech Republic.
Silva and Franca completed a 21-12, 21-18 victory over Lenka Hajeckova and Hana Klapalova to cement their place at the top of Pool A in their third and final preliminary match.
The Brazilians have qualified for the last 16 without dropping a set and are viewed by many as the team most likely to dethrone May-Treanor and Walsh.
China's Xue Chen and Zhang Xi also progressed to the last 16 after enjoying an untroubled victory against Greece while, in the evening's game, Australia's Natalie Cook bowed out of her record fifth Olympic Games after the Czech Republic's Marketa Slukova and Kristyna Kolocova triumphed in a late-night thriller.
Cook and her team-mate Tamsin Hinchley needed to win this match to have any chance of reaching the knockout stage following defeats to the USA and Austria, but succumbed 21-16 18-21 15-11 to finish bottom in Pool C.
Elsewhere, Germany's Katrin Holtwick and Ilka Semmler joined the qualifiers from Pool A with a victory over Mauritius and Russia's Anastasia Vasina and Anna Vozakova sealed top spot in Pool B after a battling three-set victory over Switzerland.
In the men's competition, Brazil's Ricardo Santos and Pedro Cunha preserved their perfect start but were pushed all the way by a spirited Canada side.
Ricardo and Cunha are among the chief contenders for a medal and have booked their place in the last 16 after three straight wins in Pool F, each achieved without dropping a set.
They came close to seeing their perfect record ended as the Canadian pairing of Martin Reader and Joshua Binstock came agonisingly close to taking the match to a decider, but Brazil held on for a 21-18 24-22 victory.
'It was a great match,' said Cunha. 'Two tough sets and only a small difference of points, but finishing with three wins is the most important part.'
It was a great match. Two tough sets and only a small difference of points, but finishing with three wins is the most important part.Pedro Cunha
Russia's Konstantin Semenov and Sergey Prokopyev prevailed in a hard-fought three-set encounter with China while Poland's Grzegorz Fijalek and Mariusz Prudel defeated winless South Africa in straight sets.
Much to the disappointment of the home crowd, Britain's John Garcia-Thompson and Steve Grotowski bowed out of the men's competition with a third straight preliminary phase loss, this time against Norway.
Jacob Gibb and Sean Rosenthal of the USA bounced back from their surprise defeat to Poland to post a convincing straight-sets win over Latvia.
The American duo, currently the highest ranked team on the World Tour, looked out of sorts as they went down 2-0 to the unheralded Grzegorz Fijalek and Mariusz Prudel on Monday. But they looked back to their best today, with Gibb in particular enjoying huge success when attacking the net as the Americans rattled off a 21-10 21-16 win to move into the next round.
Julius Brink and Jonas Reckermann of Germany secured top spot in men's Pool C in the evening with a straight-sets win over Switzerland's Sascha Heyer and Sebastian Chevallier. Both teams had already qualified from the pool after each picked up wins over China and Russia in their opening two games.