Great Britain's men's basketball team lost on their first Olympic appearance since 1948, going down 95-75 to Russia in Group B at the Basketball Arena.
The host nation started in energetic fashion and led 18-17 following a three-pointer from Luol Deng.
But Russia gained control and were never threatened after opening up a 49-34 lead at the half-time interval .
"We can do better," said Deng. "We're just not here to be here, we want to compete. We came out to win the game."
GB forward Pops Mensah-Bonsu said his team "can't dwell" on the defeat.
"We'll look at the tape and bounce back. We felt our half-court defence was good and they struggled against it," he insisted.
"But when you turn the ball over and let them get baskets, it's easy for them to get a lead."
NBA all-star Deng led Britain's attack with 26 points but GB head coach Chris Finch was concerned by his performance.
"We ask Luol to do a lot for us," said Finch. "He attacked a lot, I don't know if that was a sign of frustration, but it comes from a good place. Luol maybe could have set his team-mates up a bit better."
Reigning champions the USA, strong favourites to retain their crown, powered to a 97-71 victory over France despite a lacklustre start.
Kevin Durant led the United States with 22 points. "We just played with attitude, fighting for each ball, defending hard and getting every rebound," he said. "That's how we beat teams that are hard to beat."
In the other match in Group A, Nigeria beat Tunisia 60-56.
Meanwhile, GB's next opponents Brazil earned a hard-fought 75-71 win over Australia while Spain defeated China 97-81.