Ange Postecoglou's side are given little hope of progressing out of a Group B consisting of Spain, the Netherlands and Chile, with their tournament opener against the South Americans on Friday in Cuiaba.
Western Sydney Wanderers defender Spiranovic said the Australian squad has gelled in the weeks leading into the Brazil tournament, and give themselves every chance of causing havoc in their group.
"We've been working very hard over the last few weeks to better the understanding amongst us in the defence and midfield in particular," Spiranovic told FIFA.com.
"Against Croatia there were a lot of good signs and I think the defensive structure is pretty good.
"We're going into these games as the underdogs and that's fine by us.
"Within the camp and the group there's still a lot of belief that we could go out there and surprise people.
"It's a young team and there's no fear amongst us. I'm confident we can go out there and surprise them."
Spiranovic said Postecoglou, who only took the national reins in October after German tactician Holger Osieck was sacked, has a rapport with several of his squad after linking up with them in their junior years.
Postecoglou has long been in the Australian coaching system, leading Australia's Under-20s side for seven years and worked with other junior rep sides, and Spiranovic said their knowledge of the former Brisbane and Melbourne boss would be invaluable.
"It gives you a bit of a head start if players know the coach well, know what style of football he likes to play and his philosophy," Spiranovic said.
"I played under Ange at the U17 World Cup in Peru (in 2005). It was a great experience, playing on such a big stage at such a young age is a fantastic learning experience.
"It always helps the player-coach relationship if they know each other well, and Ange has known me from a young age and I understand what he expects and requires from players, so that is only an advantage for a coach and a player."
