"Cristiano has played as a centre-forward a couple of times and scored four goals in two games," Ferguson said. "That is a great strike rate, but to score those goals as a wide player is phenomenal.
"It is a superb achievement and he has cast any doubts aside about whether he could repeat last season's total.
"Ronaldo's performance that day (last season) against Fulham was absolutely superb and he changed the face of the game.
"The winner came so late in the game, it was a plus point and a crucial victory.
"We were a few points ahead of Chelsea but as you would expect they were plodding on behind us. You knew if you made one mistake it would count."