Toby Greene snapped a last-minute goal to snatch a one-point victory for GWS over cross-town rivals Sydney in a high-scoring thriller at the SCG.
The Giants' captain was the quickest to react when the ball fell free after a throw-in deep in the forward pocket, but needed the composure to get it to his boot for the major that sealed the stirring 17.5 (107) to 16.10 (106) comeback win.
GWS kicked the last four goals of the match to overrun the Swans after trailing by as much as 24 points early in the final term on Saturday.
Greene sparked the fightback with the first of those four goals, while versatile midfielder Harry Perryman also added two as the Giants surged late.
The Swans' dashing halfback Ollie Florent was a curious match-up on Greene for much of the contest and was mostly able to nullify the Giants' dangerman near goal.
Greene still finished with four goals and had just as much impact further afield to gather 22 disposals and earn the Brett Kirk Medal for best on ground in the Sydney Derby.
"His ability to win the ball in contest is elite," Giants coach Adam Kingsley said.
"When you go through all the elite players in the league, they all win contest.
"His ability to do that, in critical moments also, is as good as anyone."
Stephen Coniglio (28 disposals, two goals) and Harry Perryman (21, three) were superb throughout for the Giants, while Xavier O'Halloran (15, two) and Finn Callaghan (26) were also influential in promising signs for the future.
The Giants' (3-4) key forward Jesse Hogan finished with two majors against the Swans' returning key defender Tom McCartin.
Young on-ball bulls Tom Green (31 disposals, 13 tackles) and Chad Warner (29 touches, one goal) were engaged in an enthralling duel in a pointer to a match-up to watch for years to come.
Toby Bedford made an immediate impact in his GWS debut after 16 matches with Melbourne, taking a diving mark in the forward pocket then nailing the set shot for the opening goal of the game.
Sydney Derby specialist Luke Parker looked set to inspire the hosts to their own comeback victory as he was crucial early when the misfiring Swans battled to stay with the Giants through the first half.
The Swans co-captain gathered 33 disposals and booted an important final-term goal, but lacked support around the stoppages to stem the flow of goals as the Giants stormed home.
"He was outstanding," Swans coach John Longmire said.
"I thought our leaders were really good, they had a good crack right across the board and he was one of them."
Lance Franklin took a while to warm into the match but got off the leash with three goals either side of the main break after Giants defender Jack Buckley had the better of their clash early on.
Key forward Logan McDonald and high-flying Will Hayward also finished with three majors, but the Swans will rue missed opportunities near goal that could have put the margin out of reach.
The Giants will head to Canberra to host rivals Western Bulldogs on Saturday night, while the Swans will face a preliminary final rematch against Collingwood at the MCG on Sunday.