(CNN) -- For about 13 minutes, Team USA sat at the top of its World Cup soccer group, ahead of the mighty Germany and star-powered Portugal.
Then Portugal struck back. With seconds left to play, Cristiano Ronaldo set up a header for his teammate Silvestre Varela, leaving the final score tied at 2-2.
It was a harsh blow for the Americans, but it does not end their World Cup dreams -- it just makes them harder to achieve.
With every team in Brazil now having played two matches, most groups now have clear winners and losers.
But not Group G. In theory, any of the four teams in the group of Germany, the United States, Ghana and Portugal could still qualify for the knockout round.
Here's how it could work for the United States.
It plays Germany, the group leader, on Thursday. Third-ranked Ghana plays Portugal at the same time.
If the United States beats Germany:
The Americans qualify for the knockout stage. Team USA would get three points for the victory, giving it seven. No other team in the group can match that, so the Americans go through to the next stage.
Is that likely?
It's possible, but it's not likely. Germany is the No. 2-ranked team in the world, and it hasn't lost a game yet this World Cup. The Americans haven't lost a game either, though.
If the United States ties with Germany:
Both teams go through to the knockout stage. Each would get a point for the draw, giving them five points each. No matter who wins the Ghana-Portugal match, neither team can end up with more than four points.
Is that likely?
The odds aren't bad. Ghana held Germany to a draw Friday, proving that it can be done.
Germany and the United States have each won one and drawn one.
If the United States loses to Germany:
It's bad, but even that's not necessarily game over. Germany would definitely finish at the top of the group, and second place would depend both on how badly the Americans lose and what the margin of victory is in the Ghana-Portugal game.
If the two teams draw, then the Americans come in second place.
If Portugal wins by a narrow margin, USA still comes second in the group and goes through.
But if Ghana wins by two or more, it'll be the Africans and not the Americans who advance -- making this the third World Cup in a row where Ghana eliminates Team USA.
The situation isn't nearly as complicated in the groups that are playing Monday, but two of the matches will decide if Brazil, Mexico or Croatia end their World Cup runs.
Brazil plays Cameroon -- which has already been eliminated -- in hopes of sealing its place at the top of Group A. Even if Brazil loses, it is likely to finish in the top two in its group.
At the same time, Mexico plays Croatia. The winner is likely to come in second place in the group, and the loser is done -- unless Croatia is the winner and Cameroon crushes Brazil. If you can find a bookie to lay you odds on that outcome, take it. If it happens, you'll end the day very rich.
That said, the only previous time the two countries have played each other, Cameroon won 1-0. Samuel Eto'o scored the winning goal in that match, back in 2003.
The Cameroon match will be Brazil's 100th in World Cup history. It's the second team to reach the milestone, after Germany did it last week.
Earlier Monday, the Netherlands plays Chile to see who comes first and who comes second in Group B.
Both teams go through either way, with the first-place team facing the second-place team from Group A (probably either Brazil or Mexico.) The second-place team in Group B starts the knockout stage by playing the top team from Group A.
Also on Monday, Spain plays Australia for the booby prize in Group B. Neither team can qualify for the round of 16, so it's only pride on the line.
The two sides have never played each other before.
Here's a quick catch-up on which teams have already qualified for the knockout stage and which ones cannot:
Bosnia and Herzegovina