Premier League - Fergie delighted at comeback win
"It was a very good performance in terms of our football, I couldn't believe we were 2-0 down at half-time," the United boss said.
"But the players kept their heads, kept playing football and got the result they deserved. They have courage to keep the ball and are not admitted by tough tackling."
Ferguson's decision at half-time to replace the experienced Rio Ferdinand, Nemanja Vidic and Michael Carrick paid dividends as new signing Phil Jones, Jonny Evans and young midfielder Tom Cleverley tore into the City defence.
"The difference the young lads made was outstanding," United striker Wayne Rooney said.
"We never know when a game is finished. Of course they are going to try and fight us for the title. They scored two goals from nowhere but we showed character to win the game."
One concern for Ferguson was the performance of his new Spanish goalkeeper David de Gea who was stranded when Joleon Lescott nodded in David Silva's teasing free kick and slow to react when Edin Dzeko's ambitious 30-metre strike flew past him just before halftime.
"It was bending a bit, it's difficult to say if he should have done better," Ferguson said.
City manager Roberto Mancini, charged with the task of ending United's domination of English soccer and bringing the league title to the club for the first time since 1968, admitted his side had been outplayed.
"They were better than us but sometimes in football if you cannot score you give the other team a chance. We were 2-0 up so it is not good to lose from this position," he said.
The Italian denied, however, that United gained a psychological edge with their impressive victory.
"I don't think it has given United a mental edge but it will be important for us to know why we lost this game," Mancini said.
"A top team doesn't always play well, but when we score two goals and go 2-0 up, we need to have a strong mentality.
"If we play another strong squad like United, or against someone like Real Madrid in the Champions League, we need to continue to play football. We need to stay high up the pitch, not go too deep like we did in the second half."
United begin the defence of their Premier League title at West Bromwich Albion on Sunday, while City, whose expensive new striker Sergio Aguero was an unused substitute in the Community Shield, host promoted Swansea City next Monday.