Chicharito struck both goals in United's 2-1 defeat of Champions League opponents Marseille last night.
Ferguson said: "I think we are surprised. When we bought him we thought it would take him some time to adjust first of all.
"He has adjusted to the physical part very well and he is lasting 90 minutes very well now.
"That has given us great options because we look at the main strikers as Wayne (Rooney), (Dimitar) Berbatov and Hernandez. With Hernandez's form the way it is we can make some changes now.
"Hernandez's pace and movement is helping us. He is real handful. You see the first goal, they boy's movement is fantastic.
"Wayne is enjoying the freedom behind Hernandez and is in really good form at the moment."