Alan Richardson's Saints are celebrating back-to-back wins either side of their bye after a horror 11-week winless stretch that may have threatened the coach's job.
Jack Billings (24 disposals, nine inside
But there were contributors galore for the Saints.
The exciting Jade Gresham booted four goals, Jake Carlisle (22, nine marks) shut down in-form Melbourne forward Tom McDonald and Jack Steven, Jack Sinclair, Shane Savage and Seb Ross ran rampant.
Sinclair won a game-high 30 possessions, while Steven accumulated seven clearances to go with his 27 touches and Jack Steele blanketed Clayton Oliver and Jack Viney at different times.
St Kilda couldn't pierce Melbourne's defensive wall in the opening 10 minutes and conceded six quick inside
But the Saints, far from panicking, rolled their sleeves up and got to work from there.
They beat the Demons at their own game, or at least limited the damage in those strength areas, while repeatedly punishing them on turnover and dominating on the outside.
Melbourne was left wanting once it became a foot race, again bringing into question the club's stocks away from the contest.
The AFL's No.1 contested ball team trailed the Saints at three-quarter time in that area (105-106), too often coughed up the Sherrin in dangerous spots and many of its forward-50 entries were 'kick and hopes'.
It may have been worse if not for ruckman Max Gawn's sterling display, highlighted by 25 disposals (13 contested), 11 marks, 39 hit-outs, four clearances and five inside
Prime movers Viney (six) and Dom Tyson (three) combined for nine disposals in the first two quarters, while Jesse Hogan was largely invisible to that stage.
Viney lifted significantly with 14 of his 26 disposals in the final term as Melbourne mounted a fightback, but it was too little too late.
In Hogan, Melbourne's coaching staff has an aerobic 195cm weapon, but is he worth more roaming further afield or taking bulk contested marks inside 50, like his first two seasons?
Tyson's raking pass to set up a strong Hogan grab in the final term saw the spearhead slot the second of his three goals – all in the second half – and slash St Kilda's lead to just 10 points.
But the Saints' composure came to the fore again, with David Armitage wonderful kick to Josh Battle creating what was effectively the sealer.
Jack Steven, after outpointing Oscar McDonald in a one-on-one contest at the top of the goal square as good as made sure of it four minutes later.
Melbourne's once-promising season is in danger of falling apart in an all-too-familiar scenario in the wake of a shock two-point defeat to struggling St Kilda at the MCG on Sunday.
The Demons, as high as third a month ago, are on the verge of tumbling out of the top eight – and will be if North Melbourne accounts for Essendon.
Three late Melbourne goals, the last to Jordan Lewis after a score review with 30 seconds remaining, made things interesting before the Saints hung on for an 18.11 (119) to 18.9 (117) victory.
The Demons, who have not qualified for the finals since 2006, have now lost six of their last eight contests at the home of football and three in a row.
Melbourne: The Demons appeared to escape unscathed.
St Kilda: Key defender Nathan Brown left the field for good five minutes into the third quarter with a left hamstring injury.
The Demons are back at their home away from home in the Northern Territory – this time Darwin – to host Fremantle on Saturday night. St Kilda is also venturing interstate to take on the Power at Adelaide Oval.
More to come
MELBOURNE 4.2 9.3 11.6 18.9 (117)
ST KILDA 4.3 11.6 14.10 18.11 (119)
Melbourne: Fritsch 4, Harmes 3, Hogan 3, Brayshaw 2, Petracca, Tyson, T.McDonald, Neal-Bullen, Melksham, Lewis
St Kilda: Gresham 4, Membrey 4, McCartin 2, Savage, Steele, Clark, Newnes, Armitage, Billings, Battle, Steven
Melbourne: Gawn, Brayshaw, Harmes, Viney
St Kilda: Carlisle, Billings, Gresham, Sinclair, Steele, Steven, Armitage
St Kilda: Brown (hamstring)
Official crowd: 38,910 at the MCG