Popovic, who has a remarkable record of eight wins, three draws and one loss, revealed he'd previously been unhappy with how his charges had gone away from physicality in the first games of his tenure.
Australia ruffled some feathers in recent friendlies against Canada and the United States with their aggression and physicality.
"Maybe we surprised them. I don't think that there are any malicious tackles, or if there was VAR in the games, that we'd have any issues in the games. It's just they didn't like the physicality," Popovic said.
"We are coming to Canada: we're supposed to respect them as a 'better nation'. We're supposed to respect the US, and we're supposed to just accept whatever happens.
"But if I think of all the qualifying games and even the first game against New Zealand, I think we actually lacked what we've always had as a nation in football and even in all codes: that we are tough, we are resilient, we are hard to beat, we are hard to play against.
"Through that, we've tried to develop football, to play better football, but we can't forget what makes us, what's our DNA. We've gone away from that.
"I felt against Japan and Saudi Arabia, they were tougher than us. They were physically better than us. They won the first challenge. They won the second challenge.
"Even though we won the two games, it's an area that disappointed me in the games and I thought the first game against New Zealand, to an extent, we almost got bullied in the game. And I can't fathom that - how that can happen with Australians.
"It was just nice to see the players being aggressive, but playing well (against Canada and the US). We had good moments ... but we're here to win. And we shouldn't forget that side of us."
Popovic noted the world's best teams didn't compromise when it came to winning duels or applying pressure, in a clear message ahead of upcoming friendlies against Venezuela and Colombia.
He wants his team to challenge the underdog narrative around Australian football.
"I feel we're building a squad and a lot of potential that in years to come, can hopefully shed that tag of just the underdogs," he said.
"We shouldn't forget or lose that toughness that Australians bring, and that desire and that willingness to win and fight, that spirit should always remain there.
"With these young players, emerging players coming through, the talent and the qualities that they have, individual skills can make us hopefully a force in years to come.
"But saying I want to do something special is just we just don't want to have limits.
"We just don't want to pigeonhole ourselves into 'let's be competitors at the World Cup, and let's go home and pat each other on the back for being there.'
"I want us to aspire for more. And I know the players believe that, and they want to aspire for more."
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