MELBOURNE, Sept 4 (Reuters) - Australia coach Ange Postecoglou has an unshakeable faith that his Socceroos will feature at next year's World Cup but says the team must maintain a relentless pressure in Thursday's final qualifier against Thailand.

The Socceroos have backed themselves into a corner after Thursday's 2-0 defeat by already-qualified Japan, who top Group B with 20 points, four more than Australia and Saudi Arabia.

Australia must win big against Thailand to give themselves their best chance of securing a fourth successive World Cup appearance, rather than slip into the tricky playoff zone.

"We have just got to play well," Postecoglou said on the eve of the match at the Melbourne Rectangular Stadium.

"If you don't play well you leave things to chance, and we don't want to leave things to chance.

"We've got to make sure we stay focused and play our football, keeping it at a high tempo and pressuring the opposition from start to finish.

"When we do that things tend to fall into place."

The Socceroos will have to wait to know their qualifying fate until Saudi Arabia host Japan hours later.

Australia will expect their forwards to fire against Thailand but Postecoglou said he would not harp on the need for goals.

"You can't start a game thinking that way. You can start getting a bit anxious," he said.

"But I'm confident of goals.

"If we win, and win well, we will put pressure on the opposition to get a result."

The importance of the occasion was not lost on veteran forward Tim Cahill, who promised a "fearless" display against the Thais.

"We all know what's on the line," said the 37-year-old, Australia's most prolific scorer.

"This is a massive moment for our country to stake a claim in a World Cup. I feel we're ready.

"Goals will definitely come. I'm confident we'll score a lot of goals and I'm confident that we'll make a great account of ourselves."

Australia will be boosted by the return of midfielder Aaron Mooy, who was a late withdrawal from the Japan match.

Striker Tomi Juri should also be fit to start against the Thais after he carried an injury into the clash against the Samurai Blue and spent most of the match on the bench.

(Reporting by Amlan Chakraborty in new Delhi; editing by Ian Ransom) ((amlan.chakraborty@thomsonreuters.com; +91 11 3015 8022; Reuters Messaging: amlan.chakraborty.thomsonreuters.com@reuters.net: Twitter: @Amlan_Reuters))