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Wayne Rooney, Javier Hernandez and Paul Scholes all started the game, and for most of the match, they put immense pressure on the Blackburn net.
However, they were not able to capitalize on their opportunities, giving Blackburn a distant hope.
So, just like that, Ferguson is able to call upon players such as Ryan Giggs, Danny Welbeck and Ashley Young—three players who were able to directly change the game. Giggs immediately presented a new dynamic on the wing, Welbeck offered fresh legs up top and Young scored the goal that secured the three points.
It is not often that a team is gifted with this kind of depth. Generally, if your best players are not up to the challenge that day, you as a manager just hope that the rest can create something.
That's not the case at United, though. I have little doubt that every single player on the bench knows they can be just as good as anyone on the pitch. Not necessarily because they have the talent, but because Fergie has instilled them with the confidence that they are champions.
Roberto Mancini should take a look here and see that depth is not created by having £50 million on the bench. Depth is a product of having a well-rounded team—something United has always done better than anyone.