The 17-year-old, who scored his first senior goal for the club last weekend to see off Aston Villa at the death, did the trick once again to kill off Sunderland's brave fightback at the Stadium of Light.
He was in the right place at the right time to deflect home Michael Carrick's shot as it sped through a crowded penalty area and clinch three precious points.
The win took United back to the top of the table after Liverpool briefly unseated them earlier with a 4-0 win over Blackburn.
Ferguson said: "He has got something special about him, the boy. I haven't seen the goal, but one of the players said he actually tried it.
"He side-footed it as it came to him. It's that quick-thinking that goalscorers have got. He has just got that instinct."
The Scot revealed he did not need to say anything to the Italian teenager as he pitched him into an increasingly frenetic battle.
Asked what his instructions were when he was asked to replace Dimitar Berbatov with 75 minutes gone, he replied: "Nothing. He knows the role we want him to play. We want him to penetrate in behind them.
"He has got good movement, he has got quickness in his movement and it showed that when he came on.
"He wasn't fazed by anything. Right away, he got involved in the game and he had a good 20 minutes for us."