Melbourne have shocked premiership favourites Hawthorn at the MCG by recording a 29-point win to blow the race for the AFL's top four wide open.
The Hawks were denied a 10th straight victory by a determined Demons outfit on Saturday afternoon, reducing their buffer at the top of the ladder to just one game.
If the three-time reigning premiers - who face North Melbourne and West Coast in the next fortnight - slip up again, they risk throwing away hosting rights in week one of the finals.
Coach Alastair Clarkson will rue sloppy goal-kicking, with his side losing 17.8 (110) to 11.15 (81).
There could also be further ramifications for the Hawks, who suffered their first defeat against Melbourne since 2006.
James Frawley was a late withdrawal for the Hawks because of a jarred shoulder, and fellow defender Ben Stratton played no part in the second half due to a shoulder injury.
The match review panel is likely to scrutinise two incidents involving Cyril Rioli, who returned with a bang - and a bump - as he threatened to drag his side over the line.
Rioli caught Clayton Oliver high in the first quarter, and he dumped Neville Jetta in a bruising tackle during the second term.
"Cyril might still get a week but if Oliver stayed down or came off the ground it might be a much harsher penalty," AFL legend Wayne Carey said on Triple M.
"Oliver's got a hard head. He bounced up and played on. That helps Cyril a lot.
"The lifting tackle will be looked at ... he's playing aggressively."
Rioli, who missed the Hawks' preceding win over Carlton because of injury, laid 12 tackles and booted four goals, including a clutch effort in the fourth quarter that put his team in front.
The Demons responded with the final five goals of the game, including two from Dom Tyson.
Midfielders Tyson, Nathan Jones and Jack Viney were magnificent for Melbourne, while ruckman Max Gawn produced arguably the highlight of his incredible season.
Gawn clutched eight contested marks, tallied 41 hit-outs and booted a goal in a best-on-ground performance.
Melbourne helped keep Hawthorn in the contest early, with six of the Hawks' seven goals in the opening half coming from turnovers.
The Hawks steadied and hit the front in the third quarter but Melbourne continued to show dare and dash, with Gawn and Aaron Vandenberg converting set shots late in the third term.
Hawthorn forward Jack Gunston, usually a sharpshooter, finished with 2.4.