Needing a win to maintain their slim hopes of a wild card spot, GWS kicked nine straight goals as they charged to a 16.15 (111) to 7.15 (57) victory at Engie Stadium.
However, Carlton's draw with the Bulldogs later on Sunday afternoon made it impossible for both GWS and St Kilda to finish 10th.
Even before the result of Carlton's game was known, GWS coach Adam Kingsley noted where the blame would rest if his team missed out.
"We've had plenty of opportunities across the course of the season and there's no one to blame but us," Kingsley said.
GWS turned a 16-point first-quarter deficit into 35 and 47-point leads at half and three-quarter time.
West Coast slumped to a 10th straight loss despite winning the clearances and racking up the same number of inside 50s.
Their lack of accuracy across the two middle quarters proved costly with GWS kicking 8.5 to 0.9.
With questions over the futures of Toby Greene, Jesse Hogan and Jake Stringer, GWS showed they had other goal-kicking options up forward, though Green contributed two majors.
Callum Brown booted four goals, Aaron Cadman three and Harvey Thomas and Riley Hamilton two each.
Both teams kicked five goals in a frantic first quarter in which West coast had seven more inside 50s.
The Eagles dashed to a 16-point lead on the back of four straight goals, with Tom Cole involved in all of them, as the visitors scored primarily from back half chains.
GWS retaliated by kicking four of the last five goals of the term to lead by one point at quarter time, with four majors coming from clearances.
The Giants carried the momentum Into the second quarter, kicking. 6.2 to 0.5, with their running game and drive from the back half cutting the Eagles apart.
"I thought our backs were outstanding, their ability to minimise scores to force poor shots, to win the ball back in contest and then to generate some attack for us, I thought they were brilliant," Kingsley said.
"Connor Idun led the way in that space."
GWS defenders Lachie Ash and Lachie Whitfield tallied 36 and 33 touches respectively and racked up 867 and 631 metres gained respectively.
"Their two half backs in particular killed us, I think they had 40 touches In our forward 50 which is an enormous amount of the ball. We just couldn't stop them," Eagles coach Andrew McQualter said.
"I thought our defensive intent just wasn't at the level its been
"Combine that with 2.14 after quarter time, the accuracy was a problem again."
Eagles spearhead Jake Waterman had another mixed outing, kicking 2.3 and Liam Baker also kicked two goals.
Teammates Tim Kelly and Harley Reid gathered 28 and 25 touches respectively and both had eight clearances.
10°C