Irish bantamweight John Joe Nevin was beaten in the second round of the Olympic boxing tournament by Badar-Uugan Enkhbat of Mongolia.
Nevin, 19, was beaten 9-2 by the 2007 world silver medallist.
Ukraine's Vasyl Lomachenko remained on target for featherweight gold after outpointing Bahodirjon Sultonov of Belarus 9-1 at the Workers' Gymnasium.
And Russia's Alexey Tishchenko beat Australia's Anthony Little 11-3 in round two of the lightweight category.
Tishchenko is trying to become the first boxer in nearly 30 years to win gold in two different weight classes.
Lomachenko, who beat world champion Albert Selimov of Russia in his first bout, demonstrated an exciting mix of skill and floored his opponent with a crunching left with 41 seconds remaining in the fourth round.
However, the 20-year-old could be tested in the quarter-finals by China's Li Yang, who advanced with a controversial 6-5 points decision over Ecuador's Luis Porozo.