Ferguson said: "The boy has got everything.
"We are expecting goals from him all the time and I don't think he ever made a mistake today. He was absolutely perfect, a marvellous performance by him."
After an equally determined success over Tottenham yesterday, Arsenal ensured United could not really afford to drop points at the start of the festive programme.
"You do worry because time was running out but my experience is to never give up on this team because they have scored so many important goals late on," said Ferguson.
"Thankfully we got the penalty. The temperament and confidence Cristiano has shown since he was a kid surfaces at times like that.
"He composed himself and took the spot-kick very well."