In a game of precious few chances, the challengers beat the champions 1-0 with a knock-out blow from Vincent Kompany's head on the stroke of half-time. The United boss was disappointed with the defending for the decisive moment - and for his players' failure to seriously attack Joe Hart's goal at the other end.
"It was a feisty, competitive game which we expected," summarised Sir Alex. "There were not a lot of goal chances. I think David De Gea's made the only save in the match. We're disappointed we never tested their goalkeeper to be honest. Our crossing was poor.
"I thought City were more of a threat than us, simply because they had more action around our box. We had control in some parts of the game but not enough to cause any damage.
"If you lose a goal at a setpiece at this level of football then you only have yourself to blame for that. It was a bad time to concede a goal because there was nothing really happening at the end of the first half."
The game had opened with United's five-man midfield looking bright but providing Wayne Rooney with some useful ammunition proved difficult, just as City found it hard to break through the Reds' eight or nine outfield players behind the ball.
"We started off quite well for maybe 10 to 15 minutes and looked as if we were on top in terms of possession and creating opportunities around their box," reflected Sir Alex.
"But as the game wore on, nothing really happened. They had a lot of possession outside our box