News broke hours before kick-off that the Huddersfield Town star would be left on the bench, in a massive selection bombshell from coach Ange Postecoglou.
The decision was widely met with disbelief and frustration as it reverberated around social media throughout the afternoon.
Mooy, who was named man of the match in last Thursday's first-leg 1-1 away draw in Malaysia, revealed he'd had an inkling he wouldn't start the match during training on Monday.
But he said the coach offered no reason for his omission.
"Yesterday we did team shapes, but stuff can change overnight," Mooy said.
"I sort of knew the day before.
"I don't make the decisions, I've just got to try my best when I play."
Initially reluctant to dish out criticism, the softly-spoken 27-year-old eventually made his feelings clear.
"Of course I was angry that I wasn't playing," Mooy said.
"Every player should be angry that they're not playing.
"But once the game got started it was just like another game, I was motivated and wanted to win like every other player on the team."
Ironically, Mooy was thrust into the action after just 10 minutes when left wing-back Brad Smith suffered a hip injury, and went on to play a key role in setting up both Tim Cahill's goals in the 2-1 extra-time win.
At first he thought calls for 'Azza' were directed at Aziz Behich, a like-for-like replacement for Smith.
Deployed higher up the field than usual, he conceded Postecoglou's tweaked three-at-the-back system was slightly baffling.
"The formation was a different today, three No.10s and one sitter," Mooy said.
"I hadn't seen it either, but it was the boss's idea and we all believe in it and go with it.
"We've just got to be a little but more clinical, it can make a big difference to the team's confidence.
"But we won the game (because) Timmy (Cahill) came out with two special moments.
"We're not over-the-top happy but we got the job done. We did it the hard way but we still got it done and we've got a big opportunity now to go to the World Cup.
"It's going to be difficult in the next round."
Postecoglou was unapologetic when asked about Mooy's exclusion.
"It's just a decision on selection," the coach said.
"We wanted to be a little bit more aggressive in attack and Aaron was the one to miss out.
"It's not the first time he's missed out and it won't be the last time.
"Unfortunately Smithy struggled with his injury and unfortunately we had to make a change.
"I guess that's the beauty of having depth in the squad, you can throw someone like Aaron on."