Some comments here on Uruguay-South Korea at the half and on USA-Ghana later.
South Korea come out playing a 4-4-1-1 (for you new to soccer and curious, that is counting where players line up at the start from the rear going up the field and not counting the goalkeeper), slightly different from a 4-4-2 as they have played all tournament, against a versatile Uruguay team now in a 4-2-3-1 after having changed it up throughout the tournament as few teams can do and succeed.
Matching up against such a common formation as a 4-2-3-1 with a 4-4-2 or something close in my opinion is very tough as the South Koreans saw against Argentina and as I have seen with other teams not just in this tournament.
All the same the side who dicatates formation changes from the norm for the opponent has an additional advantage from the start before the whistle is blown, but I don't think such was the reason for Argentina's goal via a header by a negligently unmarked striker from a cross early in the match.
For you all relatively new to soccer who are gridiron football fans as well, in American football terms this is akin to an underdog team playing a favourite by switching between games to a 3-4 defence from a 4-3 or from a ball control offence to a spread set or vice versa. Sure the players may have practised in such formations, but far more than likely they are not up to game speed on it and by default at a slight disadvantage at the very least in most cases based on that modification alone.
Adjustments at the half for South Korea back to a 4-4-2 with a substitution with another forward playing further up?
I point this out for this early game because the USA play a 4-4-2 and that is like certain other teams like England the ONLY formation they play well and consistently. Ghana all the same without any goals from other than penalty kicks in this tournament play a 4-2-3-1 consistently and well. It's far easier IMHO for any team to go back to a 4-4-2 classic English formation from another one than to go the other way.
IMHO this means the USA must be able to score early against their weak keeper or risk conceding yet another early goal due perhaps to lack of familiarity against such a formation if not some other reason as we shall see should the fast Ghana team manage up front against a somewhat weak half of the USA defence with Bocanegra and Bornstein appearing to be in to the left.
I am LESS optimistic if the now apparently way overrated central defender Onyewu plays, as only in the match against Algeria without him did we not concede a goal.
Also should the USA come out in anything but a 4-4-2, as I would see as unlikely, I will be far more pessimistic as well. Other names to instill pessimism IMHO for Team USA are Clark, Torres, and Bornstein.
Typing whilst in my role today as desk chair coach here at "work" all alone, one way that the USA might mitigate the 4-2-3-1 is by having Dempsey and a central midfielder (the versatile forwards playing midfield Edu or Buddle or TBD) cheat up more on the attacks as they have the left fullback playing behind them cheating up to the midfield more.