Lopez earlier beat Kayaalp, who ousted him in last year's World Championships finals, and he continued to impress in the medal decider, lifting the Estonian off the mat in a first-round par terre.
Nabi could not lift his opponent in the second round and Lopez held on to the surface for victory.
Only Alexander Kolchinsky and Wrestling great Aleksandr Karelin had retained the super heavyweight crown before today, and Lopez admits he could be tempted to carry on in an attempt to claim even more success at Rio 2016.
'I am thinking of going to Rio," he said. 'Maybe if all goes well, I think I could win another one.
'I am nearly 30 already and I've had three Olympics behind me and it is going to be a little bit more difficult, but life goes on.
'I don't know how long I can go on wrestling but today was a really good fight.'
Kayaalp and Johan Euren both won bronze medals after winning in the finals of the repechage.