The 18-year-old defender made an assured and composed start to his international career in a scrappy 1-0 win over Cameroon in Sydney on Friday.
Herrington became the youngest Australian starting defender in 45 years as the left-sided centre back in Popovic's back three.
Popovic said he had been considering holding the teenager back until Tuesday's friendly with Curacao in Melbourne but had been so impressed by his performances in training that he threw the Queensland teen in at the deep end.
"He looked really comfortable in the environment and I thought of giving him minutes in the second game but after I saw him train on Wednesday I was convinced he could start," said Popovic.
"When I saw him train, I thought, 'yes, he's 18, so you can find an excuse not to play him if you want'.
"But I thought to let him go out there. It is quite young and you've got (22-year-old) Ale (Circati) next to him, and hopefully that's a sign for the national team in the future.
"We had quite a hard session on Wednesday and he looked like he had been around for a couple of camps.
"Some boys you can see they're over-thinking every moment, 'I made a mistake, I'm with the national team, it's not good', but this kid just gets on with it."
Herrington would have found himself much further down the pecking order three months ago, but his successful transfer from Brisbane Roar to Colorado Rapids has opened the door for him to make a case for a World Cup call-up.
Throughout his tenure, Popovic has shown no aversion to making brave selection calls and Herrington will be well in the mix if he continues to start every game in the MLS.
Herrington faces a fight with Circati, Cameron Burgess, Jason Geria and Milos Degenek - as well as with Harry Souttar if he returns to full fitness at Leicester - for a shot at a World Cup berth.
"It has happened quickly and I think I've just sort of tried to take everything in my stride," said Herrington.
"It wasn't so long ago that I made my debut for the Roar, and everything has risen quickly since then but I've enjoyed the journey."
"I've obviously wanted to put my best foot forward at club level, the coach has shown he's going to put faith in young players and that was in the back of my mind."
