Despite controlling much of the match, the Scottish manager felt his men lost their composure after going behind against Chelsea in their FA Cup quarterfinal replay defeat.
Following Demba Ba’s stunning match-winning volley in the 49th minute, the Red Devils manager was left ruing his team’s performance and a defeat which has ended hopes of a domestic double.
The Scottish boss revealed that plans had been made to try and deal with Chelsea's Senegalese forward, but the league leader was still unable to stop the decisive goal and failed to mount a response after going behind.
"After that [Ba's goal] we lacked composure to win the game. We had a lot of possession but didn't really make use of it," Ferguson told ITV after the match.
"We spoke about Ba and the experience we had in Newcastle couple of years back. He scored exactly the same type of goal and we always had to be aware of the type of execution he has with his shots. We were caught napping to be honest with you and right at the start of the second half. It wasn't a good start for us."
Sir Alex admitted that his side, without the injured Wayne Rooney, failed to significantly threaten Petr Cech's goal despite controlling possession for much of the game.
"In the first half we were absolutely comfortable. They weren't a real threat to us in any way and we had one or two moments ourselves," Ferguson continued. "I couldn't really see us scoring ourselves apart from Robin van Persie who had a fantastic chance and should have scored with that and Cech had a fantastic save from Chicharito.
"We were comfortable but the goal, as it always does, decided the game."
The United manager felt his men were exposed on the break by Chelsea, with the Blues' "Three Amigos" particularly elusive, and in the end the FA cup holder’s tactics were enough to spoil Sir Alex’s afternoon.
"The counterattacks they had caused us problems," he added. "They have several little players who can sneak into pockets in midfield, like Mata, Oscar and Hazard. On the counterattack they can cause you bother."