Jermaine Beckford's first-half goal not only gave Leeds a famous 1-0 victory at Old Trafford, it also consigned the Red Devils to their first third-round FA Cup exit, and their first defeat by lower league opposition in the most prestigious domestic cup competition, since they were beaten by Bournemouth in 1984.
Ferguson could offer up no excuse, or explanation, for his side's defeat.
However, having declared he would rely on many of the younger players involved for the first leg of the Carling Cup semi-final at Manchester City on Wednesday, the Scot has had an immediate change of heart.
"We have a semi-final on Wednesday night and a lot of these players won't be playing," he said. "You have to view that performance in its right light.
"I am shocked by the performance because our preparation for the game was very good. But we never got going. The quality of the passing and whole performance was bad."
Ferguson admitted his players showed no passion for the contest.
"Leeds had far bigger appetite than us," admitted Ferguson. "Human beings can always surprise you but we didn't expect that today.
"We didn't start right, Leeds got their goal and it was something to hold onto.
"We spoke about Beckford's pace up front and we were caught napping."