The Eagles kicked 12.12 (84) to St Kilda's 11.14 (80).
Eric Mackenzie was the unlikely hero kicking two goals - double his tally for the previous 88 games.
The matchwinner from Mackenzie came with just two minutes to go, after his opponent Beau Maister lost a foot race towards goal when he tripped over.
Five talking points: St Kilda v West Coast Eagles
Maister, whose previous surname was Wilkes until he changed it recently, might consider another change soon to ensure the unlucky moment is lost to history.
He had kicked the behind seconds earlier that led to the Eagles beginning its coast-to-coast come from behind win.
The last quarter was exciting with missed goals, lead changes, dubious free kicks and crucial one on one battles throughout.
The tackling was fierce and the pressure grew as the game went on but both sides moved the ball with the certainty of a driver heading through a new town, looking for a bed after midnight.
St Kilda had led at every change through sheer will.
It wasn't as though the Saints were dominating - its hard when your ball use is unreliable, but the game was being played in their half.
St Kilda's lead came because it worked harder for longer than it's opponents.
Twice the Eagles kicked a goal right on the siren, keeping them in touch at both quarter time and half time after being outplayed for much of each quarter.
But West Coast kept coming and hit the front for the first time at the 16-minute mark of the last quarter when Matt Priddis kicked a goal after being awarded a dubious free kick.
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It looked to have the momentum having kicked four goals to one for the quarter, but the Saints immediately responded through Stephen Milne's fifth for the game.
The Saints then missed three chances to kick goals – with Leigh Montagna missing a shot on the run as Milne and Nick Riewoldt stood in the goalsquare waiting for the handball – before Mackenzie kicked the winning goal.
John Worsfold was relieved his team could head into the bye with a positive win-loss ratio.
"Today was about at the end of the game…one team, it really comes down to a bit of luck about who's in front when the final siren goes, so both teams never gave up and went at it and both teams had the chance to maybe hold onto the lead and it was us in the end," Worsfold said.
St Kilda coach Scott Watters thought his team controlled the play for most of the game before being beaten right on the siren. It made the loss a bitter pill to swallow but he was pleased with the effort.
"I loved the way we played for large portions of tonight. I'm disappointed for the players more so than anything," Watters said.
"If you play that way and you continue to grow around that type of football then you have something that you can be proud of."
The Eagles went into the game without key forward Josh Kennedy who withdrew pre-game with a calf complaint, and were also without skipper Darren Glass and opportunist Mark Le Cras.
It was hard not to imagine the void that trio's absence created.
With Quinten Lynch no longer at the club, the Eagles struggle to cover the loss of its key forwards. Jack Darling was good with three goals but he needed space to do his best work.
Not only was the trio's class missed, their ability to settle their team's anxious minds would have been helpful.
Worsfold knows he has a few players ready to return at the business end of the season.
"Yeah, we'd like to be playing better footy and have more players out there but we've got that to work towards," Worsfold said.
For most of the game the Saints leaders were better than their opponents.
Milne was lively enough to keep the scoreboard ticking over.
Nick Dal Santo was trying to regain touch across half-back, Leigh Montagna was full of running while Nick Riewoldt was playing a leadership role par excellence.
Click here to vote for the three best St Kilda players from the game
Riewoldt still works beyond the level of most, but his game has also now taken on another dimension in that he is creating space to allow others to step forward.
At one stage in the first half he positioned himself across half forward to keep the ball inside the Saints 50 and let his teammates battle things out in front of goal.
His class was missing but he was doing both his immediate job and creating the environment for growth.
He then played deeper forward after half-time and scored one goal worrying the Eagles.
The Saints were brave and in many ways better than the Eagles but when the siren rung, West Coast had just put its noses in front.
"I thought we controlled the game for most of the night," Watters said. "I think it was the second quarter but again the scoreboard doesn't lie. You have got to take your opportunities and execute when you have got control of the game."
West Coast players knew their season was on the line against the Saints. Picture: AFL Media
ST KILDA 4.2 6.7 9.10 11.14 (80)
WEST COAST 3.5 4.7 7.9 12.12 (84)
St Kilda: Milne 5, Maister 2, Stanley, Dennis-Lane, Riewoldt, Saad
West Coast: Darling 3, Priddis 2, Mackenzie 2, Embley, Naitanui, S. Selwood, Embley, Cox
St Kilda: Riewoldt, Montagna, Milne, Armitage, Maister
West Coast: S. Selwood, Darling, Priddis, Shuey
St Kilda: Wright (back) replaced in selected side by Saad, Hickey (foot) replaced in selected side by Saunders
West Coast: Kennedy (calf) replaced in selected side by Cripps
St Kilda: Jimmy Webster substituted out for Josh Saunders at three-quarter time
West Coast: Ashton Hams substituted out for Jamie Cripps in the third quarter
Umpires: Donlon, Wenn, Armstrong
Official crowd: 23,795 at Etihad Stadium