Despite scoring the decisive goal, Ferguson believed that the England international should have had more.
"He's fantastic," the Scot told Sky Sports News.
"His work rate, his movement, all the time he's on the shoulder of the defender and ready to run through and really he could have scored five today.
"I think he was through on goal four times. So he's been unlucky today, but he's got an important goal, he's continued his run of goal scoring in the first team this season – I think that's nine goals now – for a 20-year-old, he's doing really well."
United remain three points behind league leaders Manchester City after the win at the Emirates Stadium.