Plavins and Samoilovs beat Dalhausser and Rogers for the first time
Latvia caused a major upset on day one of the men's Olympic beach volleyball with victory over favourites and world champions the United States.
Latvia's Martins Plavins and Aleksandrs Samoilovs, ranked 21 of 24, beat Phil Dalhausser and Todd Rogers 21-19 21-18.
The Americans must win their next two matches in pool play to be assured of a spot in the medal round.
"Absolutely nothing went our way so we're going to have to take care of business," said Rogers.
"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?'."
The second-seeded Americans, who had won 21 straight international matches, return to the sand on Monday for the second of three pool matches against Switzerland.
Swiss pair Sascha Heyer and Patrick Heuscher overcame 14th-seeds Mariano Baracetti and Martin Conde of Argentina, who face Plavins and Samoilovs on Monday.
"I feel very good," said Plavins. "This is a wonderful place and the Americans are wonderful players.
"We're full of energy and I think we need to come down a little bit now. We need to get out of our pool first."
Samoilovs added: "Martin played like god tonight. It was perfect. We played against them (Dalhausser and Rogers) before and lost badly so we just concentrated on this game."
Earlier, defending champions Ricardo Santos and Emanuel Rego of Brazil sailed through their first match, beating Angola's Morais Santos Abreu and Emanuel Fernandes 21-8, 21-13.
Other winners were 10th-seeds Andrew Schacht and Joshua Slack, the Australians coming through 21-17 and 21-19 against Renato Gomes and Jorge Terceiro of Georgia.
Fifth seeds Reinder Nummerdor and Richard Schuil of the Netherlands and eighth-seeded David Klemperer and Eric Koreng of Germany also claimed victories.
In the women's draw, new Brazilian pairing Ana Paula Connelly and Larissa Franca found their feet after an early scare, finally beating Russia 23-25, 21-17, 15-5.
Ana Paula took some time to shake off 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 was teaming up with Franca for the first time.
"I was actually pleased to play three sets. It gave us time to find our rhythm."
Defending women's champions Misty May-Treanor and Kerri Walsh of the United States start their title defence in the first match on Sunday.