Samir Nasri put City ahead in just the fifth minute in North London on Sunday only for Andre Villas-Boas' men to reply with three second-half goals in seven minutes as the visitors saw their slim title hopes slip away.
Veteran keeper Friedel, who was on the bench on Sunday, says it felt like Roberto Mancini's side conceded defeat as soon as Clint Dempsey scored the 75th-minute equaliser.
The 41-year-old American believes their acceptance of the defeat shows the difference between City and United, who secured a 20th league title with a 3-0 win over Aston Villa on Monday night.
He told the Daily Mirror: "Football is strange. Something like that hasn't happened very often to an Alex Ferguson team, that's for certain.
"On Sunday, it seemed that if the game had gone on for another 20 minutes we'd have gone on to score five or six.
"There was a really strange feeling in the ground - from the City side, it seemed that as soon as we scored the first goal it was almost as if they were deflated and felt they had lost the game, even though it was only still 1-1.
"I don't know what goes on behind the scenes and behind closed doors there, but it's very rare to see anybody score three in 15 minutes against Manchester United, that's for sure."