The Argentine has scored three in two matches for the new boss to make it eight goals in December.
Mancini said: "I do not like to pick out individuals because we have been collectively very good in the two games we have won against Stoke and Wolves - but Carlos Tevez has been outstanding.
"He is a world-class striker who has shown that he is in top form. He is playing with a smile on his face and eight goals in the month of December is an incredible effort. Confidence is a great thing with players and especially when it comes to goalscoring."
Mancini was a top international striker himself, so has particularly enjoyed working with Tevez.
He added "Carlos' team ethic is fantastic and he has a good understanding with the players around him. His movement and pace worries defenders and he is clever too.
"He has scored 12 times already for the City since he came to the club and that is an impressive ratio."