USA is Fifa ranked 5 but probably about 12-15 in reality. Part of the thing that confuses Europeans is that it's not all about the "best players", but the best team. US plays great team ball, which compensates for their lack of flair. Ask Portugal in 2002, which "on paper" had more skill but were overplayed by the US.
I watched that Portugal-US match again yesterday. It seemed that after John O'Brien scored the first goal...Portugal was never truly the same. The mentality (at least from TV appearance) for Team Portugal was this game wasn't going to be a "walk in the park", but a game they weren't going to have any issues with. If Senegal hadn't beaten France, that game would've been the big upset in the last World Cup for group play.