Ryota Murata won Japan's first Olympic boxing gold for 48 years when he claimed the middleweight (75kg) title on Saturday with a 14-13 win over Brazil's Esquiva Falcao.
Murata claimed Japan's first boxing gold since Takao Sakurai won bantamweight gold on home soil at the 1964 Tokyo Games.
"I'm really happy but the result was really out of my control," said the 26-year-old.
"I work at a university and all my focus was on the boxing, so now I can concentrate on paying back all the teachers, students and families."
It capped a fine night for Japanese boxers moments after bantamweight Saioshi Shimizu had stood on the dais having won a bronze to claim Japan's first boxing medal since the 1968 Mexico Olympics.
Murata started well and landed several shots to take a 5-3 lead after the first round, but Falcao found his range and took the second 5-4 with the Japanese leading going into the final round to set up a tense finale.
The Brazilian earned a warning in the third and pinned Murata, the world silver medallist, on the ropes with less than 60 seconds left.
At the final bell, Murata raised both fists in the air, while Falcao, 22, trudged forlornly to his corner after the judges decided the final round ended 5-all.
"I'm very happy. I wanted a lot to achieve this moment," said Falcao, whose 24-year-old brother Yamaguchi won a light heavyweight bronze medal in London.
"It's the most important day of my career. It is very important for my family, I come from a humble family and this is very important for all of them."
Having lost in the semi-finals, Uzbekistan's Abbos Atoev and Britain's Anthony Ogogo won bronze medals.