The 22-year-old netted his first goal of the season in the 70th minute, with substitute James Milner scoring a spectacular long-range effort to seal three points at the DW Stadium.
It was just the second time Balotelli has completed 90 minutes for the defending Premier League champions this term amid continued reports of a possible return to the Internazionale.
“No it’s not true [Balotelli will be leaving in January]. It’s his first goal this season and I hope he can improve after this game,” said Mancini.
“We thought of bring Mario off but we thought he was fresher than Aguero.
“We have four top strikers but we’ve had some difficulty scoring goals like we did last season. I hope we can move on from this. The season is very long, and if a lot of teams are playing in the Champions League in February it can change everything.
“We are at the top with United at the moment but I think Chelsea can fight for the title as well.”