Amarilla did a good job, and during a final. He was always in control, and made just a few mistakes. He overacted a bit, but that is part of his style, and, apparently, he´ll never change that.
A final between Argentinians and Brazilians always requires a high level of concentration and the referee has to show that he - and not the players - is the boss. From the beginning Amarilla took control, and after two or three hard actions, he early started using cards. He had to show the red to Guiñazú because the Inter middlefielder made two big fouls and both deserved a yellow. Internacional complained but the referee did what he had to do... The Rules do not say anything about a "free time", a period during the initial 20 minutes, where players are allowed to made hard fouls with no punishment. Amarilla was correct.
10 minutes after sending-off Guiñazu, Amarilla conceded a penalty to the Brazilians. Well-knowing him, it could be thought that he intended to compensate, but it wasn´t the case. He was OK also in this decision, because Nilmar was pushed by Desábato.
There were two important mistakes: assistant Bernal invalidated two actions - Inter attacking - considering them as off-side. TV showed he was wrong.