Tevez has helped spark City back into life since his return from going AWOL this season.
Mancini said: "Carlos can find his best form like this, playing. I think his last two games that he played, he improved a lot.
"Also without Carlos we scored a lot of goals, but it is normal if you have players like Carlos you can score more goals.
"Maybe there are some moments you have two strikers that maybe are not in form, but you have another two.
"This is the difference, it is clear - but we did everything in November and December to try to take Carlo here again."