After wasting ample chances in a scoreless first half at Allianz Stadium on Friday, United bagged two goals in five minutes to stun the Glory and erase their unlikely 1-0 lead.
United appeared home when towering Japanese striker Ibusuki notched his second goal with 15 minutes to play.
Hiroshi Ibusuki's double paved the way for Western United's first win of the season. (Mark Evans/AAP PHOTOS)
It was his seventh goal in seven games against Perth.
"It's definitely an overdue win because the performances have been good," said United coach John Aloisi.
"I wouldn't say that we were clinical because we probably could've scored six, but we looked dangerous every time we went forward."
A late red card to Dylan Leonard put a damper on United's win, with the teenage defender set to miss next week's clash against Melbourne Victory after pushing Cristian Caicedo at the edge of the box.
Western United's Dylan Leonard (top) was given a red card for a push on Perth's Cristian Caicedo. (Mark Evans/AAP PHOTOS)
The Glory have now lost four of five games to begin the season and are still searching for a maiden victory under new coach David Zdrilic.
Given their league-worst goal difference (-14), Perth will fall to the bottom of the ladder if 13th-placed Brisbane Roar can beat or draw with Adelaide United on Saturday.
"It's clear that we're in a transitional phase," Zdrilic said.
"Obviously we wanted the season to start in a different way, but we're trying to fix things.Â
"This team is going to end up a lot different to where it is now, but at this moment there's got to be patience."
At 17, Leonard became the youngest goalscorer in United's short history when he made good on an inch-perfect corner from Ben Garuccio in the 60th minute.
Dylan Leonard (left) became the youngest player to score a goal for Western United. (Mark Evans/AAP PHOTOS)
It came after Trent Ostler scored only the Glory's second goal this season - and first in 339 minutes of football - from a counter-attack ignited by Khoa Ngo.
Perth threatened to fall in a heap only minutes later when Noah Botic found strike weapon Ibusuki inexplicably unmarked in the box.
The cross helped Botic redeem himself for blowing two golden chances in the first half, including when he sprayed a header into the crossbar at point-blank range.
Botic was at the centre of Ibusuki's second goal, again picking out the star recruit from the right wing.
This time Ibusuki had more work to do, beating three defenders before driving the final nail into Perth's coffin.
Western United's Sebastian Pasquali had to leave the field because of an injury to his left leg. (Mark Evans/AAP PHOTOS)
Leonard was shown a red card just before stoppage time in the second half for his contact on Caicedo, but the Colombian fired his free kick above the woodwork.
"If he pulled him, it's the right call," Aloisi said of the red card.
In the only other sour note for Aloisi's side, injury-plagued midfielder Sebastian Pasquali hurt his left leg in a hard collision with Perth's Luis Canga and needed to leave the field just before halftime.
"I don't think it's good ... he's on crutches," Aloisi said.
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