The Socceroos boss surprised many by playing Beach in place of regular captain Mat Ryan, also leaving veteran midfielder Jackson Irvine on the bench.
Popovic's faith in Beach was rewarded with an assured display from the Melbourne City keeper, who produced a string of saves on the rare occasions Turkey penetrated Australia's defensive wall.
Irvine's replacement Paul Okon-Engstler also impressed, playing in Irankunda to give Australia a lead they defended resolutely before Connor Metcalfe doubled it 15 minutes from time.
Popovic, however, dismissed any suggestion that picking Beach or Okon-Engstler was a left-field choice.
"They may be shocks for a lot of people, but not shocks within our playing group or staff because we're all working together every day and we can see the quality of these young boys," he told reporters.
"It's a team selected to perform well. You never know the result, of course, we're at a World Cup, but for me it's the performance – it's not the result ... regardless of the result, it was the right decision."
Popovic, who this week signed a contract extension to continue until the Asian Cup in 2027, also said the best was yet to come from his young charges.
"Their ceiling, they're nowhere near it because they're a young group with no experience at a World Cup, very limited experience playing for their national team," he said.
"Their ceiling should come in four or eight years really, most of these boys."
Popovic then turned his focus back to Australia's next match against co-hosts the United States, a game in which a win could well secure top spot in Group D.
He said he did not care if the Socceroos' victory over Turkey would prompt more respect from opponents.
"I don't know, nor am I concerned about that," he added.
"Maybe the perception changes slightly because we've beaten Turkey, a big nation ... but we've still got a lot of work to do and we've got to move on to the U.S. game."