Balotelli scored both goals — including a stoppage-time winner from the penalty spot — in Milan's 2-1 win over Udinese on Sunday.
Balotelli was meant to start on the bench but he played from kickoff after Giampaolo Pazzini was injured in the warmup.
"I'm really happy," Galliani added. "It was a very long deal, a dream that was tiring to follow. Yesterday it came true and for how it happened, it seems like a sign from fate: Pazzini was meant to play but he got injured and Balotelli started instead, then he could have scored after a few seconds, then he gets two ... and we catch up with Inter.
"The deal for Balotelli was really complicated, not because of Balotelli, but because of difficulty with Manchester City."
After cooly kicking in the winner, Balotelli held his arms out wide toward the crowd, as if saying, "Here I am."
It is a celebration, which will have many fans recalling former Milan great Zlatan Ibrahimovic, who left for Paris Saint-Germain in the offseason.
"Mario has the same physique, the same charisma, he has a similar presence," Galliani said. "I think he is the ideal substitute for Ibrahimovic. I don't know how many points Balotelli can get us. In any case we've started with three, even though you can't say that if Pazzini had played it wouldn't have been the same.
"But of course Mario gives us a lot, he was the player to strengthen us we wanted. The atmosphere has changed, with the fans, with the sponsors, with how we're seen by other big clubs in Europe."
"I'm happy he's returned to Italy," Prandelli said. "He's more serene, more motivated. And plus we can check up on him better, in all senses, seeing as he's in Milan.
"Even without wanting to, Mario has become an important character. What's happened to him maybe isn't coincidence but destiny. Now he really has to do his talking only on the pitch, as he did yesterday in Milan. That's what we've said in our last few telephone conversations."
Prandelli is confident Balotelli's return to Italy will see the 22-year-old fulfill his true potential, after a difficult time following his departure from Inter Milan in 2010.
"Balotelli is smiling more, he's more available, maybe he's found inner calm again," Prandelli said. "He's been suffering recently because of certain situations, he wasn't playing much.
"If he manages to stay like this for a long time he can grow further, he's got a lot of margin for improvement. We have to believe that. He's certainly one of those talents that only come about occasionally, so we have to do something extra to help him and make him become the player that we all dream about."
Prandelli hopes the duo can lead Italy's attack as well as Milan's, and also joked about the duo's similar crested hairstyles.
"If we win the World Cup with them, I'll cut my hair into two crests," he said. "The fact that they play together in their club is an advantage for the national team. It's not time to make a definitive choice, but we're giving it thought. They both have personality, character and enormous potential."