Balotelli's extraordinary, controversy-filled spell at the Etihad Stadium came to an end this week as he completed a reported £19million transfer to boyhood club AC Milan.
The move came at the end of a month of intense speculation over the fiery striker's future, which City had consistently downplayed, but ultimately it was felt the deal was in everyone's interests.
Mancini, who expressed his sadness at the 22-year-old's impending departure earlier in the week, said: "We are not happy because I think he did well.
"Maybe not in the last three or four months because he had a big problem with injuries, but he did well because he helped the team win the Premier League and the FA Cup.
"We are sad for this but this is football.
"It was difficult, it was only my decision.
"I am here, (for) the club and Mario. Also for Mario to go back to Italy to play for Milan was important.
"I believe in him and I believe to go back to Italy after two years in England is important."
Mancini was often Balotelli's fiercest critic at City but usually backed his former Inter Milan protege in the end.
The 48-year-old was determined to coax the best out of the often wayward Balotelli and even after a high-profile training bust-up last month, said he was prepared to give him "another 100 chances".
But despite Mancini's denials, rumours linking the player with Milan refused to subside and City acted once the Serie A giants' interest became concrete.
Mancini, meeting media to preview this weekend's game with Liverpool, said: "Until one week ago it was impossible, because we never received any offers.
"Instead in the last three days Milan started to talk with the club and did an offer.
"We thought it was good for everyone, probably, for Mario to have the chance to go back to Italy and play in a top club like Milan.
"We hope it will be important for him and for the club that can get back some money."
Balotelli's exit removes the considerable circus that often follows his every move from Mancini's concern.
But his faith in the player's talent has never wavered and he still expects the Italy international to become a star of the world game.
He said: "Yes, he has everything, always. He has quality. It is important he can understand this."
City are now with just three senior frontline strikers in Sergio Aguero, Carlos Tevez and Edin Dzeko. Other options include reserve team youngsters Marcos Lopes and John Guidetti.
Yet given Balotelli's recent form - he had been a peripheral figure this season, scoring only three goals - Mancini does not feel that is an issue.
He said: "Now we have three strikers. We have only Premier League and FA Cup, I think that could be enough."
Mancini added that City did not look to bring in a replacement forward before the January transfer deadline.
He said: "No, it was difficult to take another good player."