Balotelli came off the bench to inspire the Blues to a 2-0 win over Everton at the Etihad Stadium.
Until his arrival after an hour, City had been struggling to break down the Toffeemen's obdurate defence.
"Mario can make a big contribution this season. I am sure of this," said Mancini.
"His behaviour has been so-so. But he is a good guy.
"He likes Manchester City. He likes English football.
"Sometimes when he scores, he is unhappy. Today he was really happy. Today he knew he scored an important goal."