Pato struck both goals, but sparked a melee at the end of the game after constant showboating.
"I don't know what happened. I did a nice trick with the ball and they got angry. We won and played a great game," said the youngster.
Siena midfielder Simone Vergassola explained what prompted the furious outburst that saw players from both sides in a heated argument.
"Pato can play how he likes, but he must not make fun of us and do these little tricks," he snapped.
"He showed a lack of respect and I clearly said that to [Marco] Borriello, Ronaldinho and [Alessandro] Nesta.
"Pato did this gesture with his hands, waving us on to try and get the ball off him. That didn't seem very professional to me."