Roniel Iglesias of Cuba claimed a second gold medal in his fourth Olympics after overcoming Britain's Pat McCormack in the welterweight final.
Iglesias - who won bronze at Beijing 2008 and gold in London 2012 - moved up to welterweight in 2016 but was not on the podium.
However, there was no heartbreak for Iglesias this time with all five scorecards reading in favour of the 32-year-old.
Going into the third and final round, McCormack knew he needed a knockout to win gold but was unable to hurt an impressive Iglesias.
Forced to settle with silver, McCormack will be devastated but won't have any complaints about the outcome.
The Sunderland fighter had eased his way into the final with wins over Belarus' Aliaksandr Radzionau, Uzbekistan's Bobo-Usmon Baturov, and Ireland's Aidan Walsh - the last bout via walkover due to injury.
Meanwhile, Iglesias beat Japan's Sewonrets Okazawa, Delante Johnson of the United States, and Andrey Zamkovoy of the Russian Olympic Committee on his way to the final.
While Team GB have tasted defeat in their first final, it has already been a successful summer with six fighters guaranteed medals.
Alongside McCormack's silver, Karris Artingstall has won bronze and Ben Whittaker will compete for gold on Wednesday at light heavyweight.
Frazer Clarke at super heavyweight, Lauren Price at middleweight and Galal Yafai at flyweight are all competing in semi-final fights and will earn at least a bronze medal.