Spain's number one seed Joel Gonzalez Bonilla clinched Olympic gold with a 17-8 win against South Korea's Lee Daehoon in the men's 58kg final.
Bonilla led from the first score and condemned Lee to silver by flooring him with a terrific final-round head kick.
Russia's Alexey Denisenko, aged 18 years and 344 days, took bronze to become men's taekwondo's youngest Olympic medallist.
Colombia's Oscar Munoz Oviedo won the other bronze-medal match.
Double world and European champion Bonilla, 22, caught Lee with a three-point head shot, confirmed after a video replay, to lead 5-2 after the first two-minute round.
Lee, current world champion in the heavier 63kg category, reduced the deficit to 5-4 in the second before Bonilla landed a flurry of late power shots for an 8-4 advantage.
And the Spaniard maintained his four-point lead at 11-7 before dumping Lee on to the ExCeL canvas to seal his fate.
Denisenko surpassed previous youngest medallist Servet Tazegul of Turkey, who won bronze at 19 years and 330 days in Beijing four years ago, by beating Australia's Safwan Khalil 3-1 in their medal decider.
Oviedo also earned bronze with his 6-4 defeat of Thailand's Pen-Ek Karaket.