Latvia's Martins Plavins and Aleksandrs Samoilovs, ranked 21 of 24, beat USA team Phil Dalhausser and Todd Rogers 21-19 21-18 in what Samoilovs called "the best match in our career".
Rogers and Dalhausser, the tallest player at 2.06 metres, are hotly tipped for a medal in Beijing, where the crowd went wild for beach volleyball's high-energy atmosphere of blaring rock music and dancing girls.
"Absolutely nothing went our way so we're going to have to take care of business," Rogers said.
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"Phil was making uncharacteristic errors I've not seen him make in two years. He usually cracks these balls away and the crowd goes wild but even he was saying 'What's going on?'"
They return to the sand on Monday for the second of three pool matches. Earlier, defending champions Ricardo Santos and Emanuel Rego of Brazil sailed through their first match.
In the women's draw, Ana Paula Connelly took some time to shake off the jetlag, having arrived in Beijing on Friday as a last minute replacement for injured Juliana Felisberta da Silva.
"I was like a zombie this afternoon," said Ana Paula, who won an indoor volleyball bronze in 1996 and teamed up with Larissa Franca for the first time on Saturday. They finally beat Russia 23-25, 21-17, 15-5.
"I was actually pleased to play three sets. It gave us time to find our rhythm," said Ana Paula, 36.
Earlier, USA President George W. Bush paid a surprise visit to the Chaoyang complex to watch the Americans practice.
Defending women's champion Misty May-Treanor eventually coaxed the reluctant president into a rally. He managed a couple of hits.
May-Treanor and partner Kerri Walsh start their title defence in the first match on Sunday.
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