British judo pair Sarah Clark and Daniel Williams suffered defeats in their Monday morning bouts at ExCel.
Clark lost her first-round contest against Automne Pavia of France, who has lost just three times this year, on golden score in the women's judo under-57kgs at ExCeL.
Meanwhile Williams, who had been handed a bye into the second round, exited at the hands of 2008 Beijing Olympic bronze medallist Rasul Boqiev of Tajikistan in the men's under -73kgs category.
Clark picked up a passivity penalty midway through the contest but to her credit, the Edinburgh Judo Club fighter, 34, then went on the attack to put pressure on the European bronze medallist Pavia. The bout went into golden score, which the Frenchwoman got with a somewhat controversial wazari throw to end Clark's Olympic hopes at the first hurdle.
Clark at first felt she managed to turn out of the throw, and fall on her front. However, on review she accepted the defeat.
"It was definitely a score. Initially you think you have gotten off the technique, but that is why the video referees are there," said the three-time Olympian, who has dropped down a weight since the Beijing Games.
"I was positive with my performance until that point, unfortunately a slight error at the end cost me the match. The crowd helped massively and I used it to my advantage, but unfortunately it was not to be."
Clark felt she could have made an impact on the latter stages, and deliver a first British Judo medal since 2000.
She said: "You have got to put everything in otherwise you have doubts. I had none going into this, I was in the best shape of my life. There is nothing more I could have done. In the fight, I made one small mistake which has unfortunately cost me possibly an Olympic gold medal."
Williams, 23, was facing the experienced Tajikistan fighter, ranked 19th in the world. There was little to choose between the fighters heading into the last 90 seconds, when Boqiev collected a shido passivity penalty. But his experience told when he caught the Briton with a sweep to record an ippon score to end the contest with 21 seconds left.