There are many reasons why this win by the US was huge:
1. After showing a total lack of heart in opening losses to Italy (3-1) and Brazil (3-0), the US needed a miracle just to make the semis. They defeated the African champions Egypt (3-0) while Brazil shut-out Italy by the same score for the US to advance having scored more goals than Italy (you can argue that the tie-breaking process is lame, but it is what it is)
2. Spain is the #1 ranked team in the world. The USA has only won one other match in history against a top-ranked team was 1998 against Brazil. This game ended some huge streaks for Spain: 35-game unbeaten streak (ties a world record), 15-game winning streak (set a new world record), had not given up a goal in the first 3 games of the tournament.
3. USA was out-shot 11-4 by a talented Spanish squad, but made good on its only 2 shots on goal while keeper Tim Howard made 6 spectacular saves for the shut-out, despite being under heavy fire the entire 90 minutes.
Awesome, simply awesome. Team USA advances to its first final in a FIFA tournament ever against the winner of South Africa/Brazil.
USA! USA! USA!