Australia got a goal from Mathew Leckie in the 60th minute and held on for a 1-0 upset win over Denmark to make it to the knockout rounds. It is the first time the Aussies have advanced out of the group stage since 2006 and only the second time ever.

Denmark had a 52% chance of winning, according to FiveThirtyEight's World Cup math predictions.

Tunisia beat France, which had already advanced, 1-0 after replay disqualified a goal in the 98th minute by France's Antoine Griezmann. Several of France's top players did not start, including superstar Kylian Mbappe. Mbappe came on in the 63rd minute. Griezmann also came on in the second half.

The victory by Australia had already eliminated Tunisia from any chance of advancing.

France will take on the second-place team in Group C, while Australia will face the winners of that group. Group C action will take place Wednesday afternoon, including Lionel Messi and Argentina.

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.

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: