Australia meets South Korea in Brisbane on Saturday with the winner to top the group.
A draw will also be enough for the hosts to retain pole position, given they are six goals ahead of the Koreans with an impressive 8-1 for and against after two games.
"We have got another big game on Saturday and it's a game we want to play well and win and improve," Postecoglou said.
"And I will make changes again.
"I have made changes, not because I want to rest people or give people a chance.
"It's because I think we have still got guys in there who have got more to give and they're just waiting for that opportunity."
Postecoglou made three changes for the Oman encounter from the tournament-opening 4-1 victory against Kuwait.
Midfielder Mark Milligan replaced injured captain Mile Jedinak, while Matt McKay and Jason Davidson got starts ahead of James Troisi and Aziz Behich.
Photo: Matt McKay (right) was a successful inclusion in the side to face Oman. (Getty Images: Cameron Spencer)Milligan and McKay grasped their opportunity, both scoring goals, while Robbie Kruse and substitute Tomi Juric also found the net against the overpowered Omanis.
Australia held a commanding 3-0 lead by half-time which allowed Postecoglou to rest key players Tim Cahill, Massimo Luongo and Mathew Leckie in the second half.