Following a 2-0 win over Turkey and a 2-0 defeat by the United States, Australia qualified for the knockout phase at a third World Cup and second time in succession.
"One wonderful achievement, from the backing of the FA all the way through to the staff, the players, the fans. It's a special day," said Popovic.
Australia only needed a draw against the Paraguayans to advance but Popovic said his team had tried their hardest to win.
"You can have opinions on how the game was played, or what we both thought we needed, but we at no stage felt that we were playing for a draw. I thought we controlled the game quite well, and were in control, and had the better opportunities."
Popovic declined to comment on making six changes to his starting 11, saying that every player was important and that "no one is entitled to the shirt".
Australia will face the runner-up in Group G in Dallas, where they could meet any of Egypt, Belgium, Iran or New Zealand.
FIFA World Cup 2026
The 2026 World Cup is taking place from June 11th to July 19th in the United States, Canada and Mexico. The tournament features 48 national teams and is played at 16 modern stadiums.
Match schedule and times | Group tables | How to watch the World Cup | World Cup Format | Past winners of the World Cup
