When you first look at the two, you would think that this is just another walk in the park for the Brazilian, but Pettis is actually half puerto rican / half dominican and destroyed decent opponents (ben henderson).
Lets compare styles
Both excellent strikers, but very different strikers.
Aldo is a very technical stricker like Floyd Mayweather. He dissects people and uses his brains alot, he has some knockout power but seldom finishes fights. He has no high kick interestingly.
Pettis is a more high flying striker like Mike Tyson. He has alot of power behind his strikes, and is very explosive. People first look at him thinking hes just another alpha male garbage, but he always shocks the world and does it with a terrible knockout.
Verdict: Pettis ko's Aldo in 2 rounds.
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Thread: Jose Aldo vs. Anthony Pettis