Sydney are within reach of a double chance in the AFL finals thanks to a barnstorming Lance Franklin booting five goals to lift his side to a 20-point victory over GWS.
The Swans trailed for most of the derby and were behind by 21 points during the third term of the low-scoring scrap when they lifted, inspired by Franklin for the umpteenth time this season.
Franklin kicked the sealer and consistently troubled GWS, as he did while earning the three Brownlow votes last year at the same venue.
Leaders Luke Parker, Josh Kennedy, Kieren Jack and Dane Rampe also stood up as Sydney, written off as finals contenders just three weeks ago, triumphed 11.14 (80) to 8.12 (60).
John Longmire's team are now guaranteed to make it 15 finals appearances in 16 seasons. They will secure a top-four spot if they defeat Hawthorn at the SCG in the final round.
GWS co-captain Phil Davis, who played on Franklin during the first term, limped off and into the rooms during the second quarter after being crunched in a marking contest by teammate Rory Lobb.
It proved a match-defining moment.
Davis played on after halftime despite the painful hip injury but was stationed up forward because he was so badly restricted, leaving Franklin to torment Jeremy Finlayson.
"There's no shame walking off a ground knowing Franklin has probably got a hold of you. Because he's probably done it about 200 times," GWS coach Leon Cameron said.
"Jeremy has come a long way this year ... he was beating his man then all of a sudden you have to and play against one of the best player's we've seen in the last 30 years.
"He'll learn from that -- positioning, understanding -- but we probably didn't help him with the way the ball came in."
Franklin lifted his career tally to 917 goals to overtake Leigh Matthews and clamber into eighth on the VFL/AFL's all-time list.
Franklin, who was awarded the Brett Kirk medal, has struggled to train this year because of a sore heel but continues to stand up in clutch moments.
"He's done a little bit more training the last couple of weeks. We'll see how he pulls up after this," Longmire said.
"You can't map out anything, you go based on how he is feeling.
"We're not going to push it.
"He is an incredible competitor ... it was a fantastic win."
The Swans' yips threatened to prove costly but their speed and slick ball movement in the final quarter, in sharp contrast to an undermanned GWS outfit reeling from more injuries, meant they triumphed in front of a sell-out Spotless Stadium crowd of 21,433.
Davis, Ryan Griffen (hamstring), Jeremy Finlayson (foot) and Daniel Lloyd (cut eye) kept GWS's medical department, overworked throughout an injury-cursed season, busy.
Parker's high hit on Matt Buntine will be among a couple of incidents scrutinised by the match review officer.