American flyweight Rau'shee Warren started off with a strong round, but was out-pointed in the final two and lost a close bout Friday at the London Olympics.
Then, Errol Spence dropped his welterweight bout vs. Krishan Vikas by a 13-11 margin.
The losses left the United States without a boxer in any of the men's draws.
The No. 3 flyweight seed, Warren had received a bye into the second round but fell to France's Nordine Oubaali by a 19-18 decision. Russia's Misha Aloian, the top seed, moved into the quarterfinals, as did Great Britain's Andrew Selby. Selby is the second seed and world No. 1.
Also in the welterweight class, world No. 1 Taras Shelestyuk of the Ukraine advanced, as did the British Freddie Evans and Canadian Custio Clayton. Evans took out fourth-seeded Lithuanian Egidijus Kavaliauskas, to whom he had lost at last year's world championships.