The boss cut a frustrated figure at the Madejski Stadium, where his side twice came from behind to seal yet another thrilling comeback and retain top spot in the Barclays Premier League.
Victory was bittersweet, however, having conceded three soft goals to Brian McDermott’s struggling side and as a result, Sir Alex was brutally honest in match assessment after the final whistle.
“I thought it was going to be a record score in the Premier League at half-time,” the boss told ESPN and MUTV. “It was unbelievable. It was really bad defending and the worst we’ve been this season. We need to sort that out. Every time the ball came near our box you were just praying!
"We never competed for a cross, but in fairness to Reading they have great deliverers of the ball - [Nicky] Shorey whips in fantastic crosses. But we should have been doing better. We could have been battered today, but thankfully we are always scoring goals and that is rescuing us every time. Wayne [Rooney] was fantastic in the first half, as was Robin [van Persie] and Ashley Young. Ashley is right back to form and he gave them a really hard time.
"We brought Chris Smalling on which made a big difference in terms of height and defending their set pieces, though they didn’t get as many in the second half.
"We should have finished the game off with some of the opportunities that we had and it should have been 5-3 at half-time when the ball was over the line from Robin's shot. In the first half, I said to myself that it would be a miracle if