I think Arguello cheated to beat Chacon. Punch after the bell.

Keep in mind the crowd noise and they are in the middle of exchanges.
Chacon was about to go down and Alexis was trying to finish him and yes that punch was after the bell but Chacon was already way done and almost went down before that punch.

 

Arguello was behind by 1 single solitary point on two cards and ahead by 1 point on the other when the fight was stopped. I do not for one second believe Arguello hit him intentionally after the bell as claimed. The writing was on the wall for Chacon and he'd already shot his wad earlier and fell short.

 

Let's put aside for a moment the notion (more than a notion really) that Arguello was known throughout his career as a clean fighter, with nary a complaint ever lodged against him for his tactics in the ring. He made a career of winning cleanly and fairly, and that needs to be mentioned.

Even if one wrongly dismisses that, any analysis of his career should at the very least reveal that Arguello was extremely patient and fought with the confidence of knowing the ebb and flow of a fight in the heat of battle. He quickly sussed out an opponent's strength, reserves, ring IQ, and intangibles galore, and applied his game plan accordingly. In short, he didn't need to cheat. He had the utmost faith in his abilities to think on the fly and solve puzzles. If the plan he intended to put into action took longer than the average armchair warrior may have thought appropriate, that's okay. He knew more than we do.

And as we see in his list of achievements, he was on top of things.

 

Chacon showed good,but when the punch happens, Arguello had already loaded and shot all his arsenals on Chacon,rocking him multiple times in the round,no matter if the post bell punch happens or no the next round were definitely not good news for him.