Japan have won an appeal after Satoshi Shimizu's controversial bantamweight defeat by Magomed Abdulhamidov, of Azerbaijan.
Shimizu has been declared the winner and goes forward to the quarter-finals.
He trailed 12-5 going into the final round but on five occasions he knocked down his opponent, who also received a two-point penalty.
However, judges scored the round 12-10 to Shimizu, which was not enough to stop Abdulhamidov claiming the win.
Referee Ishanguly Meretnyyazov, from Turkmenistan, has been expelled the International Boxing Association (AIBA) said.
The AIBA said the contest should have been stopped.
"I was shocked by the final scores. He fell down so many times," Shimizu said.
"Why didn't I win? I don't understand."
No extra points are awarded for knockdowns but the verdict was still greeted with boos at London's ExCeL Arena.
Japanese officials marched to the competition office with the 500 US dollars needed to lodge an appeal.
Shimizu added: "I did do my best. I performed really well. England is the place of boxing and the spectators supported me so well so I am very pleased about that.
"This is a very memorable moment. I don't understand why the judgement went against me so I don't know how to improve."
There was more controversy in the heavyweight section when Iran's Ali Mazaheri was disqualified in the second round of his fight against Cuba's Jose Larduet Gomez after receiving three warnings for holding within a minute.
Mazaheri said: "I have never seen such a thing in the world. I could have won the bout but I had three warnings in a minute. I was not doing anything wrong."