Balotelli looked disinterested and had little impact as the champions breezed past a poor Sunderland side.
In fact City looked a much better bet after Super Mario was replaced by title hero Sergio Aguero who added a vital second minutes later.
Mancini said: "Mario worked a lot, he had a chance, I am happy with Mario.
"Mario played a good game but I think he can do better.
"When Sergio came on he was fantastic. He's scored one goal, he had another chance and played very well."
Mancini headed straight home to Italy after the game but his coach David Platt added: "I don't know why Mario went straight down the tunnel. No, he wasn't injured."