Poland and Saudi Arabia have kicked off at Education City Stadium in Doha, Qatar.

Saudi Arabia shocked the football world this week with a 2-1 over Argentina, one of the favorites to win the World Cup. Poland played Mexico and earned a scoreless draw against the squad to take one point away from the match.

The second Group C match of the day will take place later on where Mexico can eliminate Argentina from the competition with a win.

Australia and Tunisia played a tight game throughout with each squad having their chances to score but it was Australia who ultimately prevailed 1-0 over the North African side.

Tunisia is now on the backfoot when it comes to qualifying for the knockout rounds but they have not formally been eliminated in the loss to Australia. Australia have garnered three points in their two matches thus far. Tunisia has earned one point in their matches. Denmark takes on France later today in the other Group D match.

Mitchell Duke scored the only goal of the first half -- a spectacular header in the 23rd minute -- as Australia leads Tunisia 1-0 at the break.

The match, taking place at Al Janoub Stadium in Al Wakrah, Qatar, is the second match for either squad. France is set to play Denmark later today in the second Group D game of the day.

The U.S. and England tied in their match on Friday, ending the game without scoring any goals.

To advance to the next round, the U.S. will need to win its match against Iran on Tuesday.

England won its match against Iran on Monday 6-2.

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