Originally Posted by Relentless

That happened at the main event at MMAs 'Adrenaline III Bragging Rights' on the 13th of June, 2009.... right after Sylvia had lost consecutively to Nog and Fedor. Sylvia weighed in at 310 pounds completely out of shape for that fight while Mercer was imn in much better shape and much smaller when they fought, weighing in at 256. By contrast, when Sylvia won the UFC title years earlier from Rico Rodriguez at UFC 41, Sylvia weighed in at 252 pounds. After that fight Sylvia went on to fight mostly nobodies at a variety of smaller road shows and then retired.

So your example shows us two important things:
1 - A shot former champion fighter who is 60 pounds over his prime fighting weight does not gain an advantage simply by being larger... in fact he tends to get his ass kicked

2 - A smaller fighter can knock out a substantially larger fighter if he strikes well, as Mercer did with Sylvia coming in at 58 pounds over his own weight in their fight.