Ferguson said: "Carlos was the one who turned it round for them.
"Others have a different view. I know Alan Curbishley said it wasn't just Tevez.
"But I know what league they would be in now if Tevez hadn't been there.
"Players do not always get the reception you think they should get when they go back to their old club.
Tevez returns to Upton Park for the first time since his summer switch to Old Trafford with Ferguson's praise and his new tag ringing in his ears.
Ferguson said: "Tevez has shown great enthusiasm. If he does lose the ball, he's like a Terrier going after it again.
"Carlos is a strong lad and a brave lad. You can't kick him out of a game. He's up and bouncing, looking for the ball again.
"He's got fabulous qualities, the kind people want to see.
"He has a great hunger and desire. And he gets a few knocks in games, which is partly due to the fact he's always willing to take the ball."