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:

Argentina won 2-0 over Poland, clinching its spot on top of Group C and prolonging the run for superstar Lionel Messi despite the team's shocking loss to Saudi Arabia in the tournament's opening match.

Though Poland lost, the country will advance to the knockout round as well. Mexico beat Saudi Arabia, 2-1, in its match but tied with Poland at 4 points. Poland advanced on goal differential, finishing one goal better than Mexico.

Argentina will face Australia on Saturday while Poland faces France on Sunday.

The match between Argentina and Poland has kicked off as the legendary Lionel Messi fights to stay alive in what could be his final World Cup. Argentina was shocked in the first round by Saudi Arabia, which means the team is precariously close to being knocked from the tournament in the group stage.

Argentina has made it out of the group stage in 11 of the last 12 World Cups (only failing in 2002).

Poland stands atop Group C with 4 points, while Argentina is second with 3 points after a 2-0 win against Mexico. But all four teams in the group still have a chance of advancing.

In the second match now underway, Mexico faces Saudi Arabia. After the surprising win over Argentina, Saudi Arabia could advance with a win over Mexico. Mexico would need to win and hope Poland knocks off Argentina. If Mexico wins and Argentina-Poland draw, it would come down to goal differential.

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.

Win or lose, you can always count on fans to show up -- often in the most outlandish outfits.

-ABC News' Moe Zoyari