Great Britain's men produced a battling display on their Olympic debut but were beaten by Bulgaria.
Ninth in the world rankings, Bulgaria ran out 25-18 25-20 26-24 winners at Earls Court against 92nd-ranked GB.
Team GB coach Harry Brokking said: "The team played on a whole level we have never seen. Don't forget the normal level we perform at.
"We [were] punished for every mistake we [made]. What we need to do now is cut out the mistakes that we make.
"The compliment to my team is that they showed plenty of skill, especially in the serve-reception, which is the most difficult part of the game."
Team GB's best performance came from Mark Plotyczer, who top-scored with 13 spikes and six blocks.
On Tuesday Great Britain face Australia, comfortably beaten 3-0 by Argentina, while Poland beat Italy 3-1 in the other Group A tie.
In Group B, Russia - second in the world rankings - eased to a 3-0 victory over Germany, while the United States and Brazil were equally dominant as they beat Serbia and Tunisia respectively by the same score.