Liam Ryan has produced a mark of the year contender to help lift West Coast to a 16-point win over Melbourne at Optus Stadium.
The Demons were on track to post an upset victory after opening up a 19-point lead late in the third quarter of Friday night's clash.
West Coast booted four straight goals in a frenetic comeback to briefly take the lead, before a Demons settler levelled the scores.
But with nine remaining, Ryan produced the defining moment of the match in front of 51,162 fans.
Ryan chipped the ball to Josh Kennedy outside 50m before sprinting to the goalsquare.
By the time Kennedy launched his long bomb, Ryan was in place to leap on top of Melbourne ruckman Max Gawn to take the spectacular mark.
The ensuing goal gave West Coast an important edge.
"That was a spectacular mark, we'll take that. But the work he's doing off the ball is really pleasing as well," Eagles coach Adam Simpson said. "He runs like a 24, 25-year-old mature age high half-forward.
"He's learning from one of the comp's better high half forward in Jamie Cripps in how he runs. And he's bought in."
When Jamie Cripps nailed a running goal from 55m out with six minutes remaining, the lead was 12 points and Melbourne were in big trouble.
The result was put beyond doubt when Jack Darling toed the sealer from point-blank range after Melbourne defender Sam Frost fumbled a ball on the goal line in embarrassing fashion.
The 13.7 (85) to 9.15 (69) win improves West Coast's record to 6-3.
But veteran Lewis Jetta faces a nervous wait after pinning the arms of Tim Smith and slamming his head into the turf in a strong tackle.
Melbourne are struggling at 3-6, but can be heartened by their best performance of the season.
"It was a young group that travelled to Perth and showed a lot of fight and a lot of resilience and played in the right way," Demons coach Simon Goodwin said.
The Demons won the inside 50m count 62-47, contested possessions 158-141, and the clearances 39-33.
But their wayward goalkicking came back to haunt them.
Demons ruckman Gawn tallied 56 hitouts and seven clearances in a dominant display, while Jeff Garlett booted three goals.
"Sensational. I thought he was brilliant," Goodwin said of Gawn. "He really stamped his authority on the game early and continued to work hard."
West Coast forward Kennedy finished with four goals, while Willie Rioli, Cripps, and Luke Shuey booted two apiece.
The Demons failed to even score a goal in the first half of last year's 66-point preliminary final loss.
But they took just two minutes this time around courtesy of a snap to Nathan Jones.
The contrasting styles of football made for intriguing viewing.
West Coast's slow and careful ball movement was up against Melbourne's high-risks, high-octane style.
The frenetic pressure from both sides resulted in some big bumps and bruises - and a guernsey torn to shreds.
Eagles speedster Jack Petruccelle was running at full pace when he was grabbed by Frost, who ripped his opponent's jersey clean down the seam.
West Coast suffered a blow midway through the second term when youngster Daniel Venables was knocked out after copping a hip to the head in a marking contest.
The Demons lost Alex Neal-Bullen to concussion in the third term.