Sitting on the bench at StubHub Center, Bradford Jamieson IV had a flashback to when he was a kid, perched in the stands at a Galaxy game. As the confetti of a Galaxy victory fell, he stood trying to snag the falling pieces of paper, like a dog trying to catch snowflakes. He told himself that one day he'd be on that field as part of the team.

It took only 10 years for that fantasy to become reality. A week ago, he was on that field and on that team celebrating a Galaxy victory.

Jamieson, 17, graduated from Santa Monica High in early June. On Wednesday, he gets to play against one of the best teams in the world, Manchester United, in an exhibition game in the Rose Bowl.

"I really can't explain all of this," Jamieson said. "I'm just always happy, basically."

The teenager is one of the Galaxy's newest players, signed in February after playing for the Galaxy Academy in high school. He played with Galaxy II, the team's developmental club, before earning his first playing time with the big club against Kansas City on Saturday.

It took less than four minutes for Jamieson to get an assist.

Before the season, his goal was to play against Manchester United. He had met Wayne Rooney and a few other Manchester United players a few years ago. And even though he's an Arsenal fan, he thought playing against them would be "the greatest thing ever."

Jamieson didn't think it would happen, but it will.

Galaxy Coach Bruce Arena said the intersection of Jamieson's development and Wednesday's game just happened to work out. After practicing with the first team for a couple weeks, Arena liked what he saw and bumped him up.

Wednesday won't be Jamieson's first time around soccer royalty. As a member of the Galaxy, he plays with stars such as Landon Donovan, Robby Keane and Omar Gonzalez.

"To be playing with people like them? Please. I thought that only happened in FIFA," Jamieson said.

Keane, the Irishman who has had a long and successful European career, also started playing professional soccer at 17. When Jamieson was called up, Keane told him he had all the tools to excel in pro soccer, but he was at an age where players burn out quickly.

Keane stressed that even amongst the best players in the world, some never learn how to deal with distractions.

"You're thrown into the deep end," Keane said. "You go from being a scrawny kid to playing with men. I think ability usually takes over, so it's important with someone like BJ that he has a good head on his shoulders."

Arena, too, cautions against anointing players too early. Jamieson is years away from being in his prime. It's just a matter of getting him there.

"He has the right mentality right now, but it continues to be challenging because people start talking to them and telling him how great they are, when in reality they aren't as good as they think," Arena said. "It's going to take time, and only over time can we tell what type of player he's going to be."

everett.cook@latimes.com