The Power snapped a four-game losing streak in style, winning 21.10 (136) to 13.7 (85) in Sunday's twilight game at Adelaide Oval.
With two home-and-away rounds remaining, third-placed Port can't drop out of the top four.
But GWS remain in an almighty scrap to reach they playoffs - they started the round in eighth spot but have now slipped to 10th.
The Giants - on 11 wins, the same as Western Bulldogs (eighth) and Essendon (ninth) - were blown away early as Port stacked on seven goals in a first-term blitz.
Port's midfield was dominant throughout with Zak Butters (34 disposals), Brownlow medallist Ollie Wines (29, one goal) and Connor Rozee (28) all standouts, and utility Dan Houston (30, one goal) continued his stellar season.
Power winger Miles Bergman kicked three goals in the opening quarter - key forward Todd Marshall, Willie Rioli and Jason Horne-Francis (27 disposals) all finished with three majors for the game.
GWS forward Jake Riccardi slotted four goals and on-baller Tom Green (31 disposals, two goals), Harry Himmelberg (27 touches), Toby Greene (27, two goals) and Lachie Whitfield (27) battled against the Port tide.
The Power, with Bergman running amok, amassed 7.3 to 3.0 in the first quarter.
Bergman's 11 disposals in the term featured a triple treat of goals - he'd never kicked more than two in any of his 52 previous games.
Port's onslaught continued in the second term with accurate early snaps from Byrne-Jones and Rioli followed by a Finlayson major boosting the home side's lead to 48 points.
Giant forward Riccardi scored the visitor's sole goal in the quarter as Port took a commanding 41-point lead into halftime, 10.7 to 4.2.
The Power, who play Fremantle away and Richmond at home before the finals, increased their lead to 51 points at the last change and both sides kicked five goals in the last term.
The Giants host Essendon next week before an away encounter against Carlton.
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