Vasyl Lomachenko has an almost perfect amateur record of 396-1, losing just one bout to Albert Selimov (loss that was avenged twice by the Ukrainian boxer).
But, in 2011, during the AIBA World Boxing Championship, he lost a fight to Brazil's Robson Conceição. Robson won by 20-19.
The Ukrainian Boxing Federation complained about a point deduction suffered by Lomachenko for a low-blow, and also suggested that the Brazilian boxer had committed a fault in the final round for clinching in excess.
The day after, an AIBA jury accepted the protest, overturning the result and giving Lomachenko the win.
Robson is considered the main Brazilian amateur boxer nowadays. Afther that episode, he won a silver medal in 2013 World Championship and a bronze medal in 2015 Word Championship, both as lightweight. He is also the first Brazilian classified for 2016 Olympic Games, that are going to be held in Rio de Janeiro, Brazil, in August.
That's an interview with the Brazilian fighter, where he talked about the main highlights of his career, like the winning over Vasyl Lomachenko in 2011 AIBA World Boxing Championship (which was later overturned), and also about his expectations for Rio-2016.
http://round13.com.br/?pg=conteudo&entrevista=241
Here's a link for the bout between Conceição and Lomachenko in 2011 World Championship:
https://www.youtube.com/watch?v=VAuTL3RP7kM