Gemma Howell was controversially disqualified from her opening-round clash in the women's under-63kg judo against reigning world and European champion Gevrise Emane of France.
Since switching to under-63kg earlier this year, Howell - from Wolverhampton but now fighting out of the British Judo performance institute at Dartford - won four events in a row, including two World Cup titles.
Tackling Emane at the Olympic Games may have been a step up in class, but that did not stop the Briton taking on her opponent during the opening exchanges, cheered on by the partisan home crowd.
There were boos when Howell picked up a passivity penalty with two minutes left. With less than 30 seconds to go before golden score, the fighters fell to the ground, with video referees ruling that Howell had illegally grabbed her opponent's leg, and that meant she was automatically disqualified.
Howell, though, had no complaints about the ruling, and she said: "I think it was the right decision. I was down a penalty towards the end of the fight and knew she was ahead on attacks, so I had nothing to lose.
"I felt it was a situation which a few years ago would have been fine, but it is not allowed any more. I went for it and I shouldn't have."
Howell was disappointed not to have enjoyed a more succesful Olympic debut, having battled through injury to make the British squad.
"A few months ago I wasn't sure if I would get here, but I wanted to get here for the chance to achieve gold. Maybe when I go home and look at it again I can be positive, but right now I am completely gutted."
Scottish fighter Euan Burton, 33, had once been ranked as high as fourth in the under-81kg half-middleweights, but last year struggled to make an impact at either the European or World Championships. Valois-Fortier was not the expected opposition for the Scotsman, whose profile has been raised in the run-up to London 2012.
North Arena 2 was again electric as the opponents stepped up onto the tatami for a place in the last 16. There was a defining silence, though, as Valois-Fortier produced an ippon score to end Burton's Olympic dream at the first hurdle.