Julian Green first met most of his U.S. soccer teammates just a few months ago at a training session in Europe shortly before the German-American committed to playing for the United States.
DeAndre Yedlin's two brief appearances for the national team came after the U.S. had already qualified for the upcoming tournament in Brazil.
John Brooks made his debut for the national team last summer and has just three exhibition appearances in his career.
Yet those three untested youngsters who have never played a World Cup qualifier much less on the bigger stage of the main tournament were picked for the 23-man roster ahead of more proven players like Landon Donovan, Maurice Edu and Clarence Goodson.
"They are up to the task," coach Jurgen Klinsmann said Friday. "Obviously, emotionally it's a lot to handle, but we have to run them through that process. They are ready for it."
They might need to be if the United States is to make it through a difficult group that features world powers Germany and Portugal and American nemesis Ghana.
The roster includes just five players who have played in a World Cup — Clint Dempsey, Michael Bradley, Tim Howard, Jozy Altidore and DeMarcus Beasley — and seven players 24 or younger.
Green, who turns 19 next month, is by far the most untested of the group despite being a heralded prospect on Bayern Munich's reserve team who was courted by both Germany and the United States for an international commitment.
He has just six minutes of first-team experience with Bayern Munich. He practiced two days with the U.S. team in Germany ahead of an exhibition in Cyprus on March 5 and committed to the Americans later that month.
He made his U.S. debut as a substitute in the 59th minute of an exhibition against Mexico on April 2. He got an invitation to this camp and eventually made the team ahead of Donovan, the U.S. record-holder with 57 international goals.
Klinsmann said he sees constant improvement every day from Green and that he has proven himself worthy of a spot for Brazil with his play at midfield that has impressed coaches and teammates during the training camp.
"In a soccer team, it is very simple," Klinsmann said. "They measure themselves with the quality you bring to the table, not with the age and not where you are coming from. They want to see that in the games. We played over the last 10 days a lot, a lot of small-side games, very competitive games and games that you can't hide. Julian didn't hide, not even one second."
Yedlin, 20, has only slightly more international experience than Green, getting called up for the first time for a January camp that included time in Brazil and playing as a second-half defensive sub in two exhibitions this year. He was recently pulled from a game for the Seattle Sounders for poor play.
Brooks, a 21-year-old defender for Hertha Berlin in Germany, made his U.S. debut last summer. He was benched twice this season by his club team for a poor performance in December and being unable to train last month because he was hampered by a tattoo on his back.
"He struggled the last couple of months with Hertha Berlin on and off the field," Klinsmann said. "That's a process that every young person goes through. That's why these last 10 days have been extremely, extremely important."
Klinsmann was tasked with transforming U.S. soccer ever since he was hired to replace Bob Bradley in 2011, leading him to focus on long-term goals as well as the upcoming World Cup
He signed a contract extension through the 2018 World Cup in December after the U.S. received its difficult draw. But he said the decision to keep some of the untested young players over proven veterans only had to do with what was best for the team in Brazil, even if it may help prepare the team for the next tournament in Russia.
"Jurgen is doing a couple things. While he is bringing in as much experience as he can find worldwide that has an American passport, he's also renovating the team and preparing it for the next cycle," former U.S. national team coach Steve Sampson said. "Julian Green is a good example of that. I don't expect Julian Green to see a lot of minutes, if any minutes, in this World Cup, however, just by being in that environment will bode well for him in the next cycle."
AP Sports Writer Ronald Blum contributed to this report.