Denmark, one of the sleeper picks to win the tournament, settled for a 0-0 draw with Tunisia in their first game in Group D. It was the first scoreless draw of the tournament and only the second draw -- after the U.S.-Wales on Monday.

The Danes are ranked 10th in the world, while Tunisia is ranked 30th.

Denmark held its collective breath in the 93rd minute when the referee was called over to look at VAR for a hand ball, but the ruling came back with no penalty.

When the 2022 World Cup made its debut on Sunday, it kicked off one of the most significant in-game uses of technology in sports history.

All tournament long, match balls will contain a sensor that collects spatial positioning data in real time -- the first World Cup to employ such a ball-tracking mechanism. This, combined with existing optical tracking tools, will make VAR (video assistant referees) and programs like offside reviews more accurate and streamlined than they’ve ever been.

Combining these two forms of tracking has long been a holy grail of sorts in technology circles, and FIFA’s use of the ball sensor in particular will serve as a highly public test case over the next four weeks.

For more on the technology and how it will affect the World Cup, read FiveThirtyEight's in-depth investigation.

With millions of dollars in unused beer sitting in Qatar, the company AB InBev says it will be bringing the beer to the winning country for an "ultimate" celebration.

"Where there is a celebration, there is always a Budweiser. In that spirit, Budweiser wants to bring this celebration from the FIFA World Cup stadiums to the winning country’s fans," the company said in a statement. "We will host the ultimate championship celebration for the winning country. Because, for the winning fans, they’ve taken the world. More details will be shared when we get closer to the finals."

Lionel Messi and Argentina were stunned by Saudi Arabia on Tuesday as the Saudis rallied to beat one of the tournament's favorites, 2-1.

Messi, one of the sport's all-time greats, scored in the 10th minute on a penalty kick. But Saudi Arabia came out strong in the second half with goals in the 48th minute by Saleh Al-Shehri and in the 53rd minute by Salem Al-Dawsari.

Argentina is currently third in the FIFA world rankings, while Saudi Arabia is 51st.

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