On the manager’s 70th birthday the Reds went two goals behind before rallying to equalise, only to ship a third goal with 10 minutes to play.
“It's a disappointment. We never expected that,” Sir Alex told ESPN. “We've lost two terrible goals and you can't do that in games like this.
“You can expect Blackburn to put up that sort of fight, though. They were resilient, they defended well, blocked shots on the line. They did that all day. But if you lose goals like that it gives them a big opportunity to hang on.”
The visitors were certainly under the cosh from the first whistle. United enjoyed 63 per cent possession, won 17 corners and fashioned 27 attempts at goal, forcing Blackburn players into making an incredible nine blocks, 20 interceptions and 74 clearances.
What those statistics don’t show, however, is the sluggish nature of the Reds’ play, particularly in the first half.
“We found the speed of the pitch difficult,” the manager said. “We've had really heavy rain the whole week and it's made the pitch very boggy. It was difficult to get the speed of our passing up.
“But in the second half we rallied and got back to 2-2. I thought at that point we were a certainty to win it.”
Anderson’s introduction at half-time – sent on for Javier Hernandez – helped inject urgency into the side, but with the Brazilian having missed United’s last 11 fixtures, it was a substitution Sir Alex had hoped he wouldn’t have to make.