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. star forward Christian Pulisic said Thursday he is ready to return to his team for training and is still hoping to play in the team's knockout round game against the Netherlands on Saturday.

"I'm gonna go meet now with the team and the medical staff and make a decision on [training] today," Pulisic said at a press conference. "Just kind of see how I'm feeling. Take it day-by-day right now, but doing everything in my power to be able to be out there on the field Saturday."

Pulisic suffered a pelvic contusion when crashing into the Iranian goalkeeper after knocking in the eventual game-winning goal Tuesday. He was checked out by trainers and eventually returned to the pitch before being substituted out at halftime.

He was taken to the hospital for a brief stay before returning to the hotel to greet the team returning after the win.

He said in a post on social media from the hospital that he would play on Saturday, a sentiment he echoed to Fox reporter Jenny Taft Thursday morning when he told her he'd play. Officially, he is still listed as "day-to-day."

The U.S. faces the Netherlands in the round of 16 on Fox at 10 a.m. Saturday. A U.S. team hasn't advanced past the round of 16 since 2002 when they defeated Mexico in the first knockout game before losing to Germany in the quarterfinals.