United were slipping goals regularly before Christmas.
Ferguson said: "Our awareness of the game has improved.
"In the early part of the season we were giving all these early goals away and that may have been a combination of the fact that we had defenders out.
"In the first game of the season we had to play Michael Carrick at centre-half because we had four central defenders out.
"That had its impact but in the last few weeks there has been a definite change in terms of concentration and the awareness that these games are important."