A dramatic late goal from Jeremy Cameron has reignited GWS' hunt for a maiden AFL premiership, helping his team pip flag favourites Collingwood by two points at Giants Stadium.
Toby Greene finished with a game-high three goals, while Lachie Whitfield's run and class laid the platform for his side to prevail 10.6 (66) to 9.10 (64).
It was a gutsy effort from GWS, especially given Phil Davis and Zac Williams both suffered hamstring injuries in the third term and played no further part in the contest.
The Magpies had all the momentum late and looked set to steamroll their way to victory despite a worrying knee injury for Jeremy Howe, who was arguably best on ground before a nasty collision with Jacob Hopper.
But last year's Coleman medallist Cameron, who otherwise had a reasonably quiet night, marked on the cusp of the 50m arc and close to the boundary line.
Cameron's set shot, coming with three-and-a-half minutes remaining in the game, went within a whisker of scraping the post but he successfully steered it through for a goal.
"It was an absolute clutch kick," GWS coach Leon Cameron said.
"It was a really gutsy win. They're one of the better teams in the comp."
Mason Cox slotted a quick-fire reply to cut GWS' buffer to two points, setting the stage for a frantic finish.
Veteran midfielder Callan Ward stood up with a couple of crucial tackles and Greene also lifted to ensure GWS, reeling from shock losses to North Melbourne and Western Bulldogs, registered their first victory since the COVID-19 shutdown.
"Everyone had to step up, losing two guys, and we did," Greene said.
"You take a lot of confidence from that.
"We have to keep backing it up."
Collingwood coach Nathan Buckley lamented his team's slow start.
"We showed a lot of fight ... Toby Greene made a few things happen and we gave them too many looks," Buckley said.
The scrappy nature of the contest, described as a "grunt battle" by Buckley at halftime, was largely a by-product of both teams' pressure and desperation in their first rematch since last year's preliminary final.
But a slippery and hard surface, which provided a jarring fright for visiting star ruckman Brodie Grundy when he dug his knee into the turf and created a huge divot in the first term, did not help.
Grundy dusted himself off quickly but Howe looked in agony after his knee hit the turf hard after it was accidentally clattered by a desperate Hopper.
The teams were locked at 4.4 (28) apiece at the major break before the hosts busted the match open, booting three consecutive goals in the space of six minutes early in the third term.
Collingwood, having conceded more than 40 points for the first time this season, responded in style to trim GWS' lead to a single point at three-quarter time but the home side rallied.
The gutsy slog brought a smile to the face of GWS fan Steven Waugh, among a small crowd watching at the venue.