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 minutes 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 grab.

The ensuing goal gave West Coast an important edge.

And 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 in a tackle and slamming the Demon into the turf.

Smith was one of four concussions for the match for Melbourne.

Fellow Demons Alex Neal-Bullen and Christian Salem were also down for the count, while Eagles youngster Daniel Venables was knocked out in a marking contest.

Melbourne are struggling at 3-6, but can be heartened by their best performance of the season.

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.

"We gave ourselves some opportunities with the way we played, but our accuracy hurt us in the end," Demons coach Simon Goodwin said.

"That left the door ajar, and West Coast to their credit were good enough to walk through it."

Eagles coach Adam Simpson was as excited as anyone to see Ryan's mark.

"I was on the bench. I was caught up in it as well," Simpson said.

"It's just great for Liam. He's worked his backside off the last couple of years, and he's come from a long way back."

Gawn tallied 56 hitouts and seven clearances in a dominant display, while Jeff Garlett booted three goals.

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 to West Coast.

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 Demons would have come out on top if it wasn't for their inaccuracy in front of goal.

Australian Associated Press