Christian Pulisic nearly captured the entire story of the United States’ win-or-go-home match against Iran on Tuesday in the second minute, when he took off on a dangerous-looking run forward that came to nothing.

But after 37 minutes, seven shots and five chances that generated 0.42 expected goals but no actual goals (while allowing none, none and 0.00 to Iran), Pulisic truly exemplified America’s effort in this match: He put his body on the line to score the goal that would knock Iran out of the World Cup -- and send the U.S. to the knockout round.

Read more about how the USA's change in tactics earned them the win.

-FiveThirtyEight's Ty Schalter

The Group D matches are underway Wednesday morning in Qatar with France taking on Tunisia and Australia facing Denmark.

France is already qualified for the knockout stages, so the other three teams are competing for a place alongside them. A win for Australia, currently sitting on 3 points, would automatically qualify them for the next round.

Denmark and Tunisia are sitting on 1 point each, so they need to win and get some help from goal differential to qualify for the next stage.

U.S. forward Christian Pulisic was diagnosed with a pelvic contusion after colliding with Iran’s goalkeeper during a match on Tuesday, the U.S. men's national soccer team said.

Pulisic's "status is day-to-day," the team said in a tweet.

"I’ll be ready Saturday don’t worry," Pulisic said earlier in a social media post accompanied by a photo of the superstar cheering from a hospital bed. A family friend of Pulisic confirmed the authenticity of the post to ABC News.

Pulisic, 24, was helped off the field shortly after scoring a goal in the 38th minute of the match. Pulisic collided with Iranian goalie Alireza Beiranvand during the play and remained on the ground for several minutes. He did not return to the game.

He was taken to the hospital for scans on his abdomen, the team said.

Argentina, led by the legendary Lionel Messi, faces a critical match with Poland as it attempts to qualify for the knockout rounds Wednesday.

Group C is tightly packed with Poland standing at 4 points, Argentina at 3 points and underdog Saudi Arabia at 3 points. Mexico is at the bottom of the table with 1 point, but it does have a chance of making the next round.

If Poland or Argentina wins outright, it will qualify for the next round. If Saudi Arabia defeats Mexico, it will also improbably make it to the knockout stages. But who advances otherwise gets more complicated from there.

Mexico needs to defeat Saudi Arabia if it wants to advance, but they still would need to get a helpful result in the Poland-Argentina match (either a Poland win or a draw and advantageous goal differential). A draw in both matches would put Argentina and Saudi Arabia tied at 4 points and come down to goal differential as well. Poland would win the group.

Group D is more clear. France has already qualified for the next round, so they may take it easy against Tunisia. Tunisia would need to beat France, get a draw in Australia-Denmark and win out on goal differential.

The Aussies would advance with a win against Denmark. Denmark can only advance with a win, though it would need a better goal differential than Tunisia if the African country upsets France.

Here is Wednesday's schedule:

Belgium entered the World Cup with the No. 2 ranking in the world with its so-called "Golden Generation" looking at one last chance to win the tournament. Now, the team is fighting just to advance to the knockout stage.

All eyes will be on Romalu Lukaku, the star forward for Belgium who has been recovering from a hamstring injury, to see if he can play and play well. He came on as a substitute in the squad's second game for his first action of the tournament. He'll start Thursday's game on the bench too, but figures to be an important substitute.

Belgium, currently third in Group F, faces Croatia, which stands atop the group. A win for Croatia puts them in the second round and officially eliminates Belgium. A win for Belgium would also put them through. A draw and it gets more complicated, with Morocco also in contention.

Morocco is facing off with Canada, which is unfortunately already eliminated from advancing to the knockout stage in its first World Cup appearance since 1986. At 0-2, the country would still like to get its first World Cup victory ever. Morocco would clinch a spot in the second round with a win. If both matches end in a draw, then Croatia and Morocco would go through to the knockout stage.

The second slate of games Thursday features longtime soccer power Germany fighting to stay alive. The country sits last in Group E with just 1 point. They'll need to beat heavy underdog Costa Rica just to have a chance to advance. If Germany wins and Spain beats Japan, Germany would get through.

Spain or Japan would advance with a win as they play each other. Spain would also advance with a draw, but Japan would only advance with a draw if Germany loses or ties or Germany wins and Japan has the better goal differential.

Here's the schedule for Thursday: