It didn't last long though, with Central Coast Mariners's 6-2 slaying of Melbourne Victory later in the evening seeing it reclaim the A-League's pole position.
After looking relatively comfortable in the first half at Parramatta Stadium, Glory's resistance crumbled in the 57th-minute when Mooy exchanged passes on the edge of the area before steering a left-footer past keeper Danny Vukovic with the aid of a telling deflection off Michael Thwaite.
The three points made it seven wins on the spin for the A-League newcomer - the first team to achieve the feat since Melbourne Victory in 2006 - and saw it clinch a finals place in its debut season.
It was a bitter blow for the visitor, which has picked up just four points on the road, but looked capable of adding to its tally in interim boss Alistair Edwards' second game at the helm on a soggy surface at Parramatta Stadium.
The goal pumped renewed belief in Wanderers in front of the vocal red and black cheer squad - among the 11,772 fans on hand - after failing to that point to carve out many meaningful openings against a composed and compact Glory.
Substitute Ryo Nagai squandered a golden chance to haul Perth level seven minutes from time, side-footing tamley wide with the goal in his sights.
Satisfied Wanderers coach Tony Popovic paid tribute to Mooy, saying: "I am very pleased for him. He's been knocking on the door for a few games now and he's got his reward.
"The goal was a deflection but we made our own luck with good build up play around the penalty area."
Popovic is now relishing next weekend's crunch clash with title rival Central Coast, adding: "We are certainly heading in the right direction and deserved the win, although Perth were strong and solid and made a real game of it.
"I am looking forward to testing ourselves against the Mariners."
Edwards saw plenty of positives, despite the loss and insisted Glory - which has three of its last five games at home - hasn't given up on a finals spot.
"I thought we controlled possession and the pace of the game for long periods but what was lacking was the final pass," he said.
"We won't give up on making the finals until it's mathematically impossible."