Ferguson bemoaned his side's defending as they came out on top in a 4-3 thriller against Reading to go three points clear at the top of the Barclays Premier League.
"I don't know what to make of it, the first half the defending was the worst this season, absolutely no doubt about that," he said.
"Nobody competed for the crosses, in fairness Reading have a great delivery of the ball - the boy (Nicky) Shorey whips them in, fantastic crosses but we should be doing better than that. It was terrible."
United have now won seven league games from losing positions and Ferguson was pleased with his attacking players during the opening 45 minutes.
He said: "We have the players that can rescue us and today again Waz (Wayne Rooney) in the first half was fantastic, he and Robin (van Persie) and Ashley Young were a real threat to them, they couldn't control them.
"They were terrific in the first half, Ashley was right back to form and gave them a real hard time of it - Wayne made a great pass for Robin's goal, terrific pass.
"There are a lot of plus points in the sense that they never gave in and kept going and in the second half showed a great determination to get over the line and that is what it was about today, getting over the line."