Michael Harvey's hopes of an Olympic taekwondo medal were dented by a sudden-death loss to Mexico's Guillermo Perez in the men's -58kg category.
The 18-year-old Briton had trailed the World Championship silver medallist by two points but forced the bout into an extra round by a late surge.
Harvey will get another chance in the repechage if Perez makes the final.
"It's great experience for 2012 but I wanted to go further," said Harvey, who thought he had snatched victory.
"I caught his pad but obviously it wasn't hard enough or the judges missed it. I thought I had a good chance going into that last round but obviously it didn't go the right way.
"I did well because I was up against the world silver medallist but he was there to be beaten and I'm a bit gutted that I've lost."
"Michael will be a very big surprise in 2012 and we will have a very strong team"
Great Britain head coach Nelson Miller is hopeful Mancunian Harvey will benefit from his Beijing experience.
"I think Michael performed quite well in his first major tournament," said the Cuban.
"He was quite nervous at the beginning of the first round, but it's one of the best performances from Michael.
"Michael is only 18 so this is about his preparation for 2012. Michael will be a very big surprise in 2012 and we will have a very strong team."
Sarah Stevenson, competing in her third Olympics in the +67kg category, will have to overcome 2006 World Cup bronze medallist Nadin Dawani of Jordan in her first match on Saturday.
Aaron Cook, GB's world junior champion and still only 17, will make his Olympic debut in the -80kg class on Friday.
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