The Wanderers stretched their winning streak to five - the competition's best this season - and overtook Victory to move into second spot when they downed Newcastle Jets last week.
Another win at AAMI Park on Saturday night would put the Wanderers five points clear of Postecoglou's third-placed side and well on track to book a home semi-final, which comes with a top-two finish.
Postecoglou, who nominated the Wanderers' overseas imports as a major source of their success, said the belief built by their succession of wins would make them even tougher opposition.
"They're running on that momentum now, which is a pretty powerful thing," the Victory coach told reporters on Friday.
"They're obviously playing with a lot of confidence and probably playing a little bit fearlessly because they've certainly exceeded everyone's expectations.
"They've got some good players, there's no doubt about it, particularly their foreigners."
One of those imports, Dutchman Youssouf Hersi, has scored three goals in the club's past two games.
Victory has lost striker Archie Thompson (hamstring) - who is also in doubt for the following round's clash with top-placed Central Coast Mariners - and defender Adama Traore (suspension).
But midfield linchpin Mark Milligan returns from international duty and former Adelaide United player Daniel Mullen - signed this week on loan from Chinese club Dalian Aerbin - will step straight into a central defensive role.
"Obviously we've got quite a few absences tomorrow and with seven games plus finals to go there's no point easing him in," Postecoglou said of Mullen.
"He's feeling pretty comfortable with things, he's had a good pre-season (in China) and we throw him in there."
Postecoglou said while Saturday's clash was important, he didn't believe a defeat would end Victory's hopes of claiming the Premiership and Asian Champions League berth that comes with it.