Perth had come from behind at the break to take a 2-1 lead just past the hour, courtesy of strikes from Sidnei Sciola and Rostyn Griffiths.
While Kerem Bulut pulled Western Sydney level on 72 minutes, a superb goal from Risdon in the dying minutes sealed the win for Glory and equal second place on the A-League ladder.
To help inspire his struggling side Glory, which was winless in nine matches, coach Kenny Lowe made four changes to his starting line-up, including dropping Nebojsa Marinkovic to the bench.
Western Sydney was more comfortable from the start and it went ahead on 13 minutes.
Iacopo La Rocca played the ball over the top of the host's defence and into the path of the in-form Romeo Castelen.
The Dutchman burst into the area and coolly side-footed his shot past the on-rushing Danny Vukovic to make it 1-0 to the Wanderers.
Perth showed signs of life after the interval. Griffiths rose to highest from a corner, but his head was well saved by Ante Covic.
After Western Sydney failed to clear, Chris Harold sent a firmly-hit volley narrowly wide of the Wanderers post.
Glory's pressure paid off on 54 minutes. Western Sydney was unable to deal with a deep cross and the ball feel invitingly for Richard Garcia on the edge of the six-yard box.
He looped a header over the top of Covic and Sciola was on hand to nod in an equaliser at the far post for the home side.
Western Sydney almost hit back immediately. Kerem Bulut was played through into the area and rounded Vukovic before the striker's shot from an angle struck the post.
At other end is was Harold again causing a menace. He beat his opponent to a Scott Jamieson cross, but the winger's header hit the upright.
Perth would not be denied on 68 minutes however. Once more it was high ball that caused consternation in the Western Sydney defence.
Covic came off his line from a corner, yet it was Griffiths who was first to meet it and he headed into an empty to put Glory 2-1 in front.
The lead lasted only a few minutes. Perth lost the ball deep inside its own half. La Rocca played it first time to Bulut on the edge of the area and it he slotted it past Vukovic to pull the Wanderers level.
With the clock approaching 90 minutes, Risdon picked the ball up on near the Wanderers penalty area, drove forward and unleashed an unstoppable drive into the top corner to make it 3-2 for Perth.
Glory held on for the final few minutes to secure a vital three points which lifts it to equal second with Melbourne Victory and finally ends its barren run.
"I hit it pretty sweetly. It's the best ball I've ever hit. It felt good," Risdon told Fox Sports after the match.
"I was taking the ball forward and was going a bit too quick. I had some options running on the outside. I just thought the last option was to shoot. Luckily I hit it pretty well.
"The results haven't been going our way lately. Today I was lucky to help out."
Wanderers coach Tony Popovic rued his side's missed chances in the second half.
"The overall result is tough to take. I thought we played well away from home," Popovic said.
"We got punished from set plays, and they scored a wonderful goal at the end.
"But at 1-1 we had two chances that you've really got to put away."
