Phil Davis has powered GWS past Sydney and into a semifinal, dominating Lance Franklin to help the Giants secure a 49-point upset victory at the SCG.
Davis bossed Franklin in the most important one-on-one battle of Saturday's elimination final, while returning forward Toby Greene kicked 3.3 and could have outscored the Swans if he was more accurate.
Franklin finished with 0.1 as his Swans surrendered 10.19 (79) to 4.6 (30); their season ending not with a bang but a whimper.
The Giants will face the loser of Saturday night's qualifying final between West Coast and Collingwood.
It proved a case of Buddy or bust in Sydney.
The impotent Swans were held to their lowest score from some 385 games at the SCG. It would have been their lowest score in a final if not for a couple of cheap goals late in the final quarter.
Davis was helped by the poor quality and quantity of service to Franklin but nonetheless produced one of the best games of his career.
"When you have 120 minutes on the best player in the comp over the last 20 years, you give him three goals," GWS coach Leon Cameron said.
"Phil stood up from the start.
"No doubt Lance came in with an injury cloud, we acknowledge that.
"But to keep them to four goals, our back seven collectively, it was their best performance all year."
Davis' only gaffe came during a halftime TV interview, when he quickly apologised after referring to Franklin as a "f***ing" great player.
The Giants, who had lost their past three derbies, bust the game open after halftime by kicking eight consecutive goals.
"Nothing went right for us and everything went wrong," Swans coach John Longmire said.
Longmire admitted Franklin was restricted by his groin injury but noted "once you play, you have to play".
"I don't think that was the difference in the game," he said.
"I look at the other things. There were so many of them, contested ball, ball movement ... tackling ... fumbles, the hard-ball get differential."
Josh Kelly suffered a knee injury late in the first quarter and played no further part in the match. It was one of few concerns for Cameron, whose four selection gambles all paid dividends.
Greene, who tallied 27 disposals, rivalled Davis, Lachie Whitfield and Callan Ward for best-on-ground honours.
Fit-again forward Matt de Boer and injury-prone veteran Brett Deledio were both solid, and Zac Williams looked anything but a footballer playing his first game of the season.
The crowd of 40,350, predominantly red and white, were stunned by the lopsided contest.
A stunned silence in the final term was only interrupted by boos for Greene, whose kung-fu marking style irked the home side's supporters and plenty of pundits.
GWS's inaccuracy threatened to prove costly but goals from de Boer and Harry Himmelberg helped them build a 15-point lead at halftime. They never looked back.