In the Group G competition Monday, Brazil beat Switzerland 1-0 with a late-game goal by Casemiro.

With that, Brazil has won both its matches so far in the tournament and sit atop the group.

Ghana won over South Korea 3-2 in a high-intensity match that saw the momentum change several times over.

Ghana started strong, with Mohammed Salisu scoring 24 minutes in and Mohammed Kudus at 34 minutes, bringing the score to 2-0 by halftime.

But then Cho Gue-sung of South Korea scored twice, at the 58th minute and again just three minutes later. He scored both goals on a header from a cross, the second powerful strike followed by an exuberant team celebration as it tied up the game.

Ghana met the challenge just minutes later, with Kudus scoring once more to put Ghana back in the lead.

With 10 minutes of extra time, South Korea was not able to score again as the Ghanaian team successfully defended multiple goal opportunities.

Earlier Monday, in Group G, Cameroon and Serbia ended in a 3-3 tie.

Germany and Spain ended their high-energy match in a 1-1 tie Sunday.

Both goals came late in the game, with Spain's Álvaro Morata scoring at 62 minutes and Germany's Niclas Füllkrug at 83 minutes.

Croatia handily beat Canada four goals to one. Croatia's goals were scored by Marko Livaja, Lovro Majer and Andrej Kramaric, who scored twice.

Canada's Alphonso Davies scored their sole point, the country's first in a men's FIFA World Cup, within the first three minutes of the match.

Croatia is now the top team in Group F, while Canada will not advance.

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