The 4-4 draw at home to Everton on Sunday, despite leading 3-1 and 4-2, threw the door wide open for rivals Manchester City to deny United a 20th league title but it was the not the first time this season Ferguson's defence had gone AWOL at home.
They were smashed 6-1 by City in October, then lost 3-2 at home to Blackburn Rovers on New Year's Eve.
With one more home match to go they have already conceded 19 league goals at Old Trafford this season, their worst record since the start of the Premier League.
An inability to keep the ball out of their net at home also sabotaged their European campaign with Basle drawing 3-3 and Benfica 2-2 as United bowed out of the Champions League at the group stage.
Even in the Europa League Ajax Amsterdam won 2-1 in Manchester before Atheltic Bilbao returned with a 3-2 victory.
Ferguson praised his side's attacking play against Everton but did not hold back on his defenders.
"To give away four goals at Old Trafford in a home game like that which was so important to us is unbelievable. I can't believe it," he said.
"Defensive lapses have cost us. In previous matches recently we've actually defended very well. But this was a bad performance defensively.
"I think the goals we conceded were soft goals."
The absence of Nemanja Vidic since December has not helped United's cause with Rio Ferdinand badly missing his central defensive partner at times.
Yet despite United's regular home blips, they will still head to the Etihad Stadium on Monday for a title showdown with a three-point lead over City and their destiny very much in their own hands.
United usually respond well to setbacks and they can approach the match with more options than a City side who know they must collect three points.
Even a draw for United would mean they should be able to wrap up the title with games against Swansea City and Sunderland to come whereas City must travel to Champions League chasing Newcastle United for their penultimate game.
However, City will be buoyed by a home record that is the envy of their close neighbours with 16 wins and one draw and only 10 goals conceded.
"I still think United have a bigger chance than us at the moment, even if we get three points in the derby we have Newcastle and QPR, which will be difficult games," City manager Roberto Mancini said after their 2-0 victory at Wolverhampton Wanderers on Sunday.
"United after us have two games that will not be easy, but not difficult like it will be for us. But we have still have a chance."
United may still hold pole position with three games left but in this most unpredictable of Premier League seasons their could still be some unexpected twists - whatever the outcome of Monday's derby.
