Boss you have to mind yourself in the minds of these big clubs (Real, Barca MU) if you score a goal on them in the first half they don't see it as a loss. They see it as a motivation to tie or win the game. Brasil Germany et al plays the same way one nil early in the game doesn't stop these teams.
Take a look at Everton with Chlesea yesterday. Everton made sure they managed the game nil all thorough the first half. In the second half they started going aggressively after Chelsea and they got results.
Moral of the story; MU staff wasn't bothered by the one nil because the thinking is that it cannot fluster their players. Two nil different story.