The 24-year old Ecuadorian winger was signed from Wigan in June and brought into replace the departing Cristiano Ronaldo which was looked at in a weird way when it happened.
"That's six goals for Antonio," said the United boss. "We're happy with that. We've always thought that's one area he can improve on.
"He is improving and his improvement is tremendous and this is an example of that. From the day he came he was a quiet young man, but he is expressing himself well. We like to see the young players come here and develop."