Fremantle's 20.13 (133) to 5.8 (38) victory keeps the Dockers only half a win away from second-placed Geelong with two rounds remaining.
Zippy small forward Hayden Ballantyne appeared to suffer an arm injury as he jogged off late in the game in pain in another possible concern for the Dockers.
The round-21 clash, which at times was little more than a training run for the Dockers, atrracted a tiny crowd of 13,768 fans at the MCG.
Ballantyne and skipper Matthew Pavlich booted four goals each for Fremantle while David Mundy dominated midfield and athletic big man Zac Clarke was also influential in the absence of Sandilands.
Nineteen-year-old Jack Viney with 28 disposals was one of Melbourne's better contributors as the Demons suffered their 18th loss from 20 games.
Melbourne's 103kg defender Jake Spencer ran with his back to the ball and crashed his forearm into Sandilands' head during a marking contest early in the first term in an incident which will be assessed on Monday by the match review panel.
The 211cm Sandilands left the field looking unsteady on his feet as blood streamed from a gash on his forehead, which appeared bruised and swollen.
Fremantle led by 27 points at quarter-time after holding the Demons goal-less in the opening term.
The Dockers slammed on another five goals in a six-minute burst to jump out to a 50-point lead at the 17-minute mark of the second term, but the Demons scored the last three goals of the half to narrow the margin to 31 points at halftime.
Fremantle stretched their lead to 58 points at three-quarter time after a five-goal third term to Melbourne's solitary major.
Nathan Fyfe's goal just before the siren, after a frustrated Lynden Dunn crashed into his back and conceded a 50-metre penalty, was one of several disciplinary lapses from the Demons in defence.
Fremantle helped themselves to another six goals in the final term to Melbourne's one behind.
The Dockers host top-eight rivals Port Adelaide next Saturday while Melbourne face Adelaide at AAMI Stadium on the same day.
Fremantle coach Ross Lyon said he was confident Sandilands and Ballantyne would be available for next month's finals series.
Lyon said Ballantyne had a wrenched shoulder while Sandilands had been taken to hospital for a scan after his head knock.
"It doesn't look great," Lyon said.
"It looks like a cheekbone (fracture). We know you can play with them potentially he (Sandilands) could miss one or two (weeks) but he'll certainly be available when the whips are cracking."
FREMANTLE 4.5 9.6 14.11 20.13 (133)
MELBOURNE 0.2 4.5 5.7 5.8 (38)
Goals: Fremantle - Ballantyne, Pavlich 4; Mayne, Hill 2; Sandilands, Silvagni, Pearce, Spurr, Walters, Fyfe, Sheridan, Clarke. Melbourne - Kent, Fitzpatrick, Howe, Viney, Davis.
Best: Fremantle - Mundy, Clarke, Pearce, Hill, Ballantyne, Barlow, Neale, Crowley. Melbourne - Viney, Sylvia, McDonald, Trengove, Terlich.
Umpires: Justin Schmitt, Gary Fila, Tristan Burgess.