It appeared Chris Ikonomidis' first-half goal would be enough to ensure Tony Popovic's first return to Wanderland was a triumphant one.
However Elrich gave a long-suffering crowd of 7,181 reason to cheer when he struck home from long-range in the 94th minute on Sunday.
The draw not only extends the Wanderers' unbeaten run to three, but ends the Glory's four-game winning streak.
They remain nine points clear of nearest rival Sydney FC atop the A-League table.
The Wanderers were seemingly destined for another despairing display in a match that also signaled the end of their unhappy move to Spotless Stadium.
Their final three home games of the season will be at ANZ Stadium.
Despite the Wanderers' struggles over the past two seasons, the league's youngest club had only lost two of their 16 matches at the Olympic Park venue.
The return of all-time leading goalscorer and games record-holder Mark Bridge also gave the club plenty of motivation to perform.
However there was little energy from the home side and their fans from the start.
A lack of atmosphere, which included another boycott of the club's active supporter group, matched a lifeless first half showing.
Their ineptitude could have been a result of coach Markus Babbel being forced into fielding a makeshift back three due to injuries and suspension.
Their plight was made worse when youngster Jordan O'Doherty was stretchered from the field after suffering a suspected ACL injury in the 14th minute.
That pain doubled not long after when Diego Castro found an unmarked Ikonomidis, who helped on a low cross under Vedran Janjetovic for the opener.
It was the former Wanderers striker's eighth goal of the season.
On the flipside, it took the Wanderers until the third minute of injury time to finally test Glory gloveman Liam Reddy, however Oriol Riera's header was palmed away.
The home side picked up their running in the second half and, coupled with Perth's inability to put the game away, slowly grew into the match.
The Glory only had two looks at goal compared to Western Sydney's eight in the second half, the last of which came from outside of the box by Elrich.
