You forgot to mention that the result established who your adversaries were going to be in the second round.You are playing against two undefeated group winners, while we are not. Sure, your enthusiasm is a little better right now, but your group is harder. So things are more complex than what you want to suggest. You shouldn't act like the way you see things is always the correct one. And enthusiasm has a upper bound, so it will be about the same in your so important semi-final.
But the result in the 2nd round establishes who the semifinal matchups will be. If the USA wins their 2nd round group, then Brazil will likely face one of those 1st round undefeated teams, Argentina or Chile, both who would like nothing more than to knock of Brazil. Meanwhile, the USA will face a team that was in 2nd place in the 2nd round.