"It was an encouraging 25 minutes then after that it was a bit of a struggle," Postecoglou said.
"We'll sit down and analyse it but I can't be too critical of the players. We've worked them really hard for 10 days and when you do that obviously they're going to play a little bit of a price in the game.
"But for a longer-term benefit, and so we can be ready for that first game in Brazil, it had to be done."
The Socceroos open their World Cup campaign against world No.13 Chile on June 13 and defence, as expected, appears the main concern.
The Socceroos' vulnerable defence was exposed when South Africa's Tokelo Rantie easily got past the back four, dispossessing Alex Wilkinson and playing the ball back to Patosi, who put the visitors in front in the 13th minute.
If an understrength South Africa can cause the Socceroos defence trouble one can only imagine what the attacking fire power of Chile, the Netherlands and Spain will do.
With Matthew Spiranovic rested with a minor ankle injury, Wilkinson combined with Ryan McGowan in the centre of defence and the partnership looked shaky.
Jason Davidson played at left back while first-choice right back Ivan Franjic, who looked the strongest of the back four, limped off the field with a knock to his right knee.
Postecoglou said after the match it wasn't "too serious".
The midfield was without skipper Mile Jedinak and veteran Mark Bresciano, who were both rested with minor concerns, and lacked the composure the experienced duo bring.
The Socceroos face two more warm-up clashes before their first World Cup game, one against a Brazilian club side and the other against Croatia on June 6.
Postecoglou says he has no intentions changing direction and feels the side is on track.
"We'll stick to course," he said.
"I think we're heading in the right direction and we'll continue to do so.
"This was part of the precess for us. We've got two more games in Brazil and all of these games are designed for us to be ready for that first game against Chile.
"After the Croatia game we'll have a full week to prepare for the Chile game and freshen the players up.
"The only time that's important for me is Chile, that will give me a good indication of where we're at.
"Before that, it's just working hard on making sure what ground we need to make up we make up."
- AAP