A brace from Rovers top scorer Yakubu was cancelled out by Dimitar Berbatov in the second half, but defender Grant Hanley headed home from a corner to earn a late victory for the Premier League strugglers.

"It is a disappointment - we can't believe it," Ferguson said. "We never expected that to happen.
 
"We have lost two terrible goals in the game and you cannot do that in games like this.

"They are fighting for their lives of course and you can expect them to put up that kind of fight. They were resilient, they defended really well and blocked shots around the goal-line all day but if you lose goals like we did, then it gives them a big opportunity to hang on."

United goalkeeper David De Gea was caught out of position by Hanley as he converted the decisive goal, but Sir Alex refused to place the blame solely on the young Spaniard.

"Yes, (De Gea could have done better), but I think we could all have done a lot better with (the third goal)," he said.

"We have got a lot of injuries at the moment but hopefully that will improve.

"We had to take a gamble on Anderson’s fitness, he has been training very well for 10 days now but obviously for his first game back it is not easy, but he didn’t let us down and did his best.

"Midfield is an area we were missing experience, like Michael Carrick and Ryan Giggs."

Despite the defeat handing the initiative to rivals Manchester City in the title race, Ferguson remained confident that his team would put the surprise setback behind them.

"We can improve on today's performance and we won't put many other displays in like that. I'm still very confident we will have a real go this season," he said.

Following the remarkable result, embattled Blackburn manager Steve Kean called for a truce at Ewood Park with the club's supporters.

The 44-year-old has faced a barrage of criticism from certain sections of the Lancashire outfit's fanbase, but the much-needed three points may have brought the Scot some respite.

The win builds on last week's 1-1 draw with Liverpool at Anfield, and Kean insists now is the time for supporters to get firmly behind the team.

"In the light of these results I hope it is time for a truce between me and fans who want me out," Kean told reporters.

"I have always respected the fans and the amount of mail we have got from Rovers fans from all over the world and other fans, just saying keep going and it has been nothing but positive messages.

"Obviously at the ground and within the local media it has been negative, which we have been really disappointed about, because it is at a time when we all need to get behind what we are trying to do and recognise how many players are not involved because they are in the treatment room.

"I have said over the last few months that the thing that sends the fans home happy are results and they have seen a result and a performance today and against Liverpool at Anfield on Boxing Day.

"But I am under no illusions that fans want to see the team win and we put pressure on ourselves when we don’t win at home and we were disappointing in our last two home games but we have turned that around."