Murata was seeded second in the draw, with Florentino fourth, and the bout was as close as may have been expected from two of the medal favourites.
The pair have met before, with Murata victorious in the semi-finals of the World Championships last year - a competition where he went on to claim silver while Florentino won bronze.
Murata was at his most active in the opening minutes, using his reach to penetrate and move into a 5-3 lead.
Florentino, so impressive in his win over Great Britain's Anthony Ogogo yesterday, responded impressively, dictating the tone in the second round with a consistent flurry of right jabs.
Murata was put on the back foot but his defence held firm and he remained 9-8 in front going into the final round.
Again, Florentino went on the attack and briefly forced his opponent into a dangerous position on the ropes before losing his footing.
Florentino made all the running but Murata was deflecting enough shots to draw the round and take the Olympic title.