Britain's taekwondo fighter Sarah Stevenson suffered a first round defeat to American Paige McPherson in the women's under-67kg at ExCeL.
McPherson landed a head shot to lead 3-0 in the first round.
Stevenson was picked off twice again, but registered with a kick to the body.
Trailing 5-1 heading into the last round, it was all or nothing for the Doncaster fighter.
The American thought she had landed two scoring head kicks, but both were chalked out on video review.
Stevenson, though, was unable to respond and her dreams of Olympic gold were over - but she can come back in the repechage if the American reaches the final.