THE MOST UNEXPECTED American star at this World Cup won’t be playing for the United States in tomorrow’s win-or-go-home game against Belgium. In fact, he doesn’t even kick a ball. Instead, he’ll be on display this afternoon, manning the middle while Nigeria plays France in a Round of 16 game in the host nation’s capital of Brasilia.

Mark Geiger, an American referee who works Major League Soccer games, has quietly been a breakout star and source of pride for both American soccer and, especially, the American refereeing community, working two near-flawless games in the group stages. Geiger and his all-MLS assistant referees—American Sean Hurd and Canadian Joe Fletcher—were chosen for the France-Nigeria match in reward for their efforts.

“He has been fantastic. His positioning has been great so he’s always in the right place to see the play and make the right call and he’s managed the personalities on the field so well and brought a calmness to the game,” said Peter Walton, a former English referee who now heads the Professional Referees Organization which oversees refs for professional matches in the United States and Canada. Walton was speaking hours before boarding a flight to Brazil where he will proudly be watching Geiger in person.

“And it’s not just Mark," he continued. "Sean and Joe have been very good and they’ve communicated very well as a team, which you need at any level, but especially a level as high as the World Cup with all that pressure and atmosphere in the stadiums. They’ve done so well and we’re so proud.”

(FIFA puts an embargo on officials talking to the media during the World Cup. Still, ASN reached out to Geiger but calls went straight to his voicemail—which was full.)

Geiger, a 39-year-old former math teacher from Beachwood, N.J., and his crew began the tournament working Colombia’s 3-0 win over Greece on June 14 and turned in a performance so flawless that Major League Soccer players—players!—were singing his praises.

Always quick to destroy refs for poor performance so lets take a sec to recognize that an @MLS ref has been best in #WorldCup so far. #Bravo

— Dax McCarty (@DaxMcCarty11) June 14, 2014

In the World Cup, officials aren’t guaranteed a second game. A poor performance and FIFA will quietly drop them from the pool of 25 center referees chosen to work games. So being assigned a second group stage match—Chile’s stunning 2-0 upset of reigning champion Spain—was itself a solid endorsement of Geiger’s performance.

To say Geiger has exceeded expectations would be a bit of an understatement. No American ref had been chosen to work the middle for either of the last two World Cups, and Geiger is the first American center ref—ever—to work a game in the knockout stages.

“To keep getting chosen, that’s a statement of how well he’s done,” said fellow MLS referee Ricardo Salazar. “They have a lot of officials to choose from and when you keep getting games in a tournament like that, that’s saying something.”

There has long been a perception in American soccer circles that the officiating development hasn’t kept up with the player development and that the American refs were sometimes out of their depth in MLS. Walton disputes this—“every country, they think their officials and referees aren’t as good as the players,” he said—but also admits Geiger’s performances in Brazil have done much to improve the perception of American referees.

“The world, in a soccer sense, is beginning to now talk about U.S. officials in the same breath as the highest refs in world soccer," he said. "That will only reflect well on our domestic level, the game here. It reflects well on all of us.”

Salazar admits rooting for his friend the way fans root for countries.

“Instead of wearing a national team jersey I wear my yellow (referee) jersey,” he joked. “But it can be nerve-wracking. One bad call and he’s done so you know that when you watch. (American refs) have needed a strong performance like this and he’s done it. He’s hit it out of the park.”

All of us at @MLS are proud of @PROreferees' Mark Geiger, the first American to referee a knockout-stage match at the @FIFAWorldCup.

— Don Garber (@thesoccerdon) June 30, 2014

Geiger has had a gradual ascension to this level. From working rec league games as a teenager for pocket change, before moving up to lower division games in the U.S. and then becoming an MLS official in 2004. He became FIFA-eligible, meaning he could do international games, in 2008 and began doing CONCACAF matches. In 2011, again with Hurd and Fletcher on the lines, he worked the U20 World Championship and did so well they were chosen to work the final. That year he was also MLS’ referee of the year.

Last year he became a full-time ref with PRO. “Mark’s paid his dues, no doubt about it,” Walton said. “But I think being full-time has let him focus on his fitness and taken that to a higher level, and really work on the nuances of officiating, and that’s what you’re seeing” in Brazil.

Salazar thinks being an educator has helped Salazar at this World Cup. “Before the tournament they tell the refs what they want them to emphasize and he is able to understand what they’re looking for and give them that on the field. He makes it look easy but luck finds you when you’re prepared.”

He also thinks this won’t be the last we see of Geiger in Brazil. “I would not be surprised if you see him at end of tournament,” Salazar said. “People say, ‘An American working the World Cup Final?’ But he’s shining a light on some guys, showing these (American) guys can referee with the best in the world. We can go anywhere on this planet and ref a game without a hitch and Mark’s proving it.”

Brooke Tunstall is a veteran journalist who has covered Major League Soccer since its initial player dispersal draft. Follow him on Twitter.