Russia's Egor Mekhontcev claimed light-heavyweight gold after a close bout with Kazakhstan's Adilbek Niyazymbetov.
The two men were tied on 15-15 and also after countback before the judges finally decided to award victory to Mekhontcev on individual preference.
"It came down to who preferred which style of boxing. Niyazymbetov controlled much of the bout with some careful boxing on the back foot but the judges preferred Mekhontcev's more aggressive style."
The Russian has now beaten Niyazymbetov three times this year despite being below him in the world rankings.
Yamaguchi Falcao Florentino
of Brazil and
of Ukraine won bronze.
Niyazymbetov, 23, started well by exploiting Mekhontcev's slow footwork with some wily shots to take the first round 4-3.
But the Russian upped the pace to take the second round 5-4 with a series of effective right-hand punches to level the bout.
Both men landed some powerful blows in the final round and there was a long debate among the judges before 27-year-old Mekhontcev was declared the winner.
He follows in the footsteps of Cassius Clay, who claimed Olympic gold in this category in 1960 before turning pro and later changing his name to Muhammad Ali.