The US plays the winner of Group H. Belgium would most likely be tougher to beat than Algeria. Going into today's matches, Group H looked like:
Belgium - 6 pts - +2 goal difference
Algeria - 3 pts - +1 goal difference
Russia - 1 pt - -1 goal difference
S Korea - 1pt - -2 goal difference
If Belgium loses, they would be at 6 points and, at most, +1 goal difference. If Algeria wins, they would also be at 6 points, but they would be at least +2 for their goal difference, so Algeria would win the group, with Belgium second.