The controversial striker came off the bench to inspire the Blues to a 2-0 win over Everton at the Etihad Stadium.
"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.!
He added: "Sometimes when he scores, he is unhappy. Today he was really happy. Today he knew he scored an important goal."
It also proved Mancini correct to introduce Balotelli ahead of Carlos Tevez, who remained on the bench throughout.
However, the City chief admitted a four-match European suspension that rules the striker out of Tuesday's Champions League trip to Bayern Munich played a part.
"I needed a player who could also play on the right side," said Mancini. "We needed to open up the defence, plus Mario can't play against Munich on Tuesday."
Everton manager David Moyes made no apology for the limited tactics, believing his team were harshly treated when a throw-in he felt should have been in favour of his side went against them in the build-up to Balotelli's opener.
"I wasn't going to come here for the enjoyment of Manchester City," he said. "I was going to come here and do what was right for Everton.
"I have to praise the players for how they went about their task. They have done a lot of really good things. For long periods we kept them at bay."
Source: PA
Source: PA