Team USA could be eliminated before it plays another game.
Because of a quirk in the scheduling, Japan plays two more games before the U.S. plays its pool finale against Mexico. If Japan beats Mexico by any margin in Tuesday night's game, then beats Korea in Wednesday's game in a relatively low-scoring affair, the U.S. would be eliminated, as the first tiebreaker in case of a three-way tie is runs allowed in common games.
The tiebreakers for the World Baseball Classic are extremely complicated, and as a function of the tournament's ties to the International Baseball Federation (the European-based baseball governing committee that seems to reflect soccer rules in its bylaws), laughably antiquated. The first tiebreaker is simply head-to-head competition, but that wouldn't apply in case of a three-team tie. In case of a three-way tie, there is a list of tiebreakers used to determine the first place team in the group. Once that is determined, second place is determined using head-to-head competition among the two remaining teams.
The second tiebreaker is runs allowed in games among the tied teams. But if that also results in a tie, the next tiebreaker is earned runs allowed in common games, which means the official scorer could be the most important person in the stadium, ruling whether a run is earned or unearned.
If that still can't break the tie, the next tiebreaker is team batting average in common games. If the teams are still deadlocked, it comes down to some version of a coin flip or drawing straws.
Still there? If so, here's a possible scenario where the U.S. would not advance.
If Japan beats Mexico and Korea, then Japan, the U.S. and Korea would all be 2-1. The U.S. edged Japan narrowly 4-3 in their Sunday game, while Korea beat the U.S. handily Monday, 7-3, giving the U.S. a runs allowed total of 10 while Korea has currently allowed 3 and Japan 4.
If Japan beats Korea in a game where the Japanese allow five runs or less, the U.S. would be eliminated, because Japan would take the top spot (fewest runs allowed), while Korea would advance because of its head-to-head victory over the U.S.
For example, if Japan beats Korea 6-3, Japan would have allowed six runs, Korea nine and the United States 10. Japan would get first place based on fewest runs allowed, while Korea would advance by virtue of having beaten the United States.
If the Mexican team beats Japan, the scenarios become less complicated. A loss would drop Japan to 0-2, which means that the U.S. could ensure a spot in the semifinals with a win over Mexico on Thursday. If Japan beats Mexico but then loses to Korea, Korea would wrap up a spot in the semifinals, while the U.S. could still advance with a win over Mexico, which would make it the only 2-1 team.