Pato made his first Serie A start in eight months and Allegri was satisfied.
Allegri said: "He put in a good performance and was often dangerous. In the last eight months he has basically played a game and a half, so it's difficult for him to find full fitness straight away. I substituted him because he was tired.
"I think Milan's 'cure' is simply an issue of results and not performances. Our worst game of the season was against Anderlecht in the Champions League."