World champion Oleksandr Usyk of Ukraine edged a tense heavyweight final with Italian Clemente Russo to claim his first Olympic gold.
In a rematch of the 2008 quarter-final, there was little to separate the two until the final round, when Usyk did enough to secure a 14-11 victory.
The defeat for Russo meant he took silver for the second successive Games.
Azerbaijan's Teymur Mammadov and Bulgaria's Tervel Pulev won bronze medals after reaching the semi-final.
When victory was confirmed, Usyk belied his stature to produce a nimble display of dancing in the centre of the ring to celebrate his victory.
Usyk becomes only the third Olympic boxing gold medallist in Ukraine's history, after Wladimir Klitschko in 1996 and Vasyl Lomachenko in 2008.
Ukraine have now won four boxing medals in London.
Denys Berinchyk took silver in men's light-welterweight, while Taras Shelestyuk and Oleksandr Gvozdyk won bronze in welterweight and light-heavyweight respectively.