The United States had gone 4-0 over the first two days of the Olympic tournament and American flyweight Raushee Warren received a bye into the second round Monday.
Browne, however, lost a close battle with Hooper, who will now take on Russian Egor Mekhonteev in the second round.
Among the anticipated second-round bouts in the light-heavyweight division will the one between China's Meng Fanlong and Brazil's Yamaguchi Florentino. They will meet Sunday.
Meng easily disposed of Ahmed Barki of Morocco 17-8 and Florentino was a 15-14 winner over Sumit Sangwan of India.