The top seed continued his winning form as he manoeuvred his kicks intelligently around the Iranian.
Bagheri Motamed tried unsuccessfully to land some kicks on Tazegul's torso but could not get past the world champion's defences.
Tazegul was ecstatic with the result, and said: 'You don't know how special it feels to take the gold back home. This is what we dream of when we take up Taekwondo.'
The first bronze was claimed by USA's Terrence Jennings, who made a comeback from the repechage and defeated Brazilian Diogo Silva 8-5.
Afghanistan's Rohullah Nikpah overcame Great Britain's Martin Stamper 5-3 to add another bronze to his collection after winning the first at the Beijing 2008 Games.