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.

U.S. national team coach Gregg Berhalter tried to keep the focus on Tuesday's game at a press conference as he faced questions about why the U.S. team's Twitter account removed the Islamic emblem from Iran's flag in a post Sunday. He also insisted his team had no knowledge of the post.

The U.S. soccer federation said it removed the logo to show support for those protesting in the country against authoritarian rule and its treatment of women.

Berhalter tried to keep the focus on the uniting power of sports and the World Cup, even as Iran called for the U.S. to be kicked out of the World Cup for altering its flag.

"Sport is something that should bring people together, bring countries together," Berhalter said. "When you look at the Olympics, to see all those countries competing at the same time, is a wonderful event. The World Cup is very similar, where people come from all around the world. Fans come from all around the world, and you get to compete on the field, as brothers, so sport does have the ability to do that."

U.S. captain Tyler Adams was criticized by an Iranian reporter for mispronouncing "Iran," which he apologized for, and he was questioned about discrimination in the U.S., saying it is everywhere but there has been progress. But he also deflected attention back to the game.

"Listen, we support Iran's people and Iran's team. But that being said, you know, we're laser focused on this match as they are as well," Adams, 23, told reporters. "We know how important this is for our progress of our team and what we want to do to prove to our country, you know, how hard we've been working. And we know they want to do exactly the same."

The U.S. must defeat Iran Tuesday to advance to the knockout stage of the tournament.

-ABC News' Karyn Rhodus