Ferguson said: "A loss of concentration from Joe cost us. He made some good saves but he is there to do a job and made a mistake.
"It shows how far we have come that we are bitterly disappointed with a defeat at Elland Road. We have to dust ourselves down. We recover well from defeats, though we don't have many.
"We are frustrated because we feel we didn't deserve to lose. Leeds fans applauded us off the pitch and if we perform like that we won't lose many games.
"George Boyd was the best player on the pitch buy miles. He was absolutely outstanding."