Walyalup has taken out a comfortable 24-point win to bring an abrupt end to St Kilda's four-game winning streak and dash the Saints' finals hopes.
The Dockers dominated the Saints from the start to win 6.9 (45) to 3.3 (21) at Fremantle Oval on Sunday.
Having been on the verge of making their first finals appearance, St Kilda (4-4) could now miss the top-eight even if they beat fourth-placed Brisbane and ninth-placed Carlton.
Dana East was everywhere for Walyalup, leading the game in disposals (19) and contested possessions (11), alongside Orlagh Lally (19 disposals, five clearances).
Jaimee Lambert was the shining light for the otherwise subdued Saints, collecting a game-high seven clearances and 13 contested possessions.
Walyalup flew out of the gates from the first siren, producing its highest-scoring quarter of the season with 26 points in the opening term.
Conversely, the score was the most the Saints have conceded in any quarter this season.
Aine Tighe set the tone for the Dockers with a brilliant goal less than 30 seconds into the first quarter, followed by two majors from Gabby O'Sullivan and another by Angelique Stannett.
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Ella Friend slotted a much-needed goal for the visitors to make it 4.2 (26) to 1.3 (9) at quarter time.
With less than a minute till the long break, captain Hayley Miller (two goals) kicked the only major of the second quarter to give Walyalup a comfortable 26-point lead at half time.
Despite goals from Tyanna Smith and J'Noemi Anderson in the second half, the Saints struggled to eat into the deficit.
WALYALUP 4.2 5.5 6.6 6.9 (45)
ST KILDA 1.3 1.3 2.3 3.3 (21)
Walyalup: O’Sullivan 2, Miller 2, Tighe, Stannett
St Kilda: Friend, Smith, Anderson
Walyalup: Stannett, Lally, Kauffman, Strom, Bowers
St Kilda: Smith, Patrikios, Lambert, McDonald
St Kilda: TBC
Crowd: TBC at Fremantle Oval