Seventeen-year-old Kristian and 15-year-old Gabriel were introduced in the 76th minute of Glory's 2-0 loss to the Red Devils at Optus Stadium on Saturday night.

Glory entered the match missing a host of their best players, forcing Popovic to draft a bunch of Academy members into his squad for the game against Manchester United.

Unlimited substitutions meant Popovic had the ability to hand game time to a host of the club's emerging youth stars, with 15-year-old Joshua Rawlins another lucky youngster to taste action against United during the school holidays.

The two Popovic brothers have already impressed onlookers with their skill and maturity at Glory training.

They each scored a goal in a recent 3-0 friendly win over Bayswater City.

Kristian also notched two substitute appearances with Glory during the last A-League season.

Coach Popovic said it was a proud moment to see his two sons play against Manchester United.

"They came on and I'm sure they'll remember it," he said.

"For sure, as a father you're proud to see that happen.

"They're still at the very baby steps of their football career. And like a lot of young aspiring players, whether they can get there or not - we'll see.

"But certainly they're boys that will give it their best. It was nice to see them out there."

Gabriel, a mad Red Devils fan who already towers over most people despite being only 15, got to swap jumpers with England international Chris Smalling after the match.

Kristian got Scott McTominay's jersey.

The brothers still live at home, and said they were enjoying playing under their father.

"He's a father off the field, but coach on the field," Kristian said.

"It's really easy to be a player under him. There is that little bit of extra motivation that he is our coach."

Popovic also had a nine-year-old son who is already impressing on the field.

Glory were forced to defend for long periods of Saturday's game, with Marcus Rashford's 60th-minute strike finally breaking the deadlock.

James Garner added the second in the 85th minute.

When asked whether he had ever coached a game where the ball had spent so much time in his defensive half, Popovic replied: "Did you expect anything different?

"It would have been different if we opened up and made it an exhibition game.

"The score might have been seven, eight, nine, 10 - because they can score at any moment. We defended very well."

Australian Associated Press