A first-half penalty from Jeff Hughes coupled with a stunning 63rd-minute strike from Chris Lines sent Millwall sliding to their first League One defeat of the season at the Memorial Stadium.
Hughes slammed home the opener on 25 minutes from the penalty spot after Andy Frampton was penalised for a foul before Lines hit an absolute screamer to wrap up the points.
Yet again Lions boss Kenny Jackett had his hands tied in terms of his preferred starting XI, with midfielder Marc Laird joining Paul Robinson and Jason Price along with a plethora of other injured first-teamers on the sidelines.
In came new-signing Danny Schofield for his debut following his transfer deadline day move from Yeovil Town, whilst striker Ashley Grimes was handed a senior start for the first time since 3rd March 2009.
Teenagers Kiernan Hughes-Mason and John Marquis were due to be on duty for Scott Fitzgerald's U18s at QPR but found themselves named on the subs' bench at the Memorial Stadium instead.
Rovers, themselves fielding debutants in the shape of keeper Mikel Andersen and Mark Wright, had The Lions under pressure from the opening whistle, forcing four corners in the opening five minutes.
Having weathered the early storm, Millwall began to ask questions of the Gas defence themselves.
Frampton and Jimmy Abdou worked a half-chance for Gary Alexander, but his path to goal was blocked by Danny Coles.
Some great work by Schofield on the right saw the right winger wriggle past Aaron Lescott and send over an inch perfect cross for Grimes. Unfortunately the latter's header lacked power and was comfortably held by Andersen.
Abdou then floated a header from Schofield's free-kick as Millwall enjoyed their best spell of the opening half.
But back came Rovers with Darryl Duffy and then Lescott thwarted in quick succession by a great defensive block from Alexander and keeper David Forde respectively.
However, there was little Forde could do to prevent the opening goal on 25 minutes. Ali Fuseini's attempted clearance just outside the danger zone was blocked, Hughes picked up the ball and broke into the area before he was floored by Frampton.
Referee Jon Moss had no hesitation in pointing to the spot, sensibly brandished just a yellow card to Frampton - and Hughes did the rest with a fierce spot-kick into the top left hand corner to put Rovers 1-0 ahead.
The Lions, looking surprisingly edgy at times defensively, struggled to get any real attacking momentum going before the break either.
That fact was clearly not lost on manager Jackett, who introduced George Friend for the subdued Dave Martin, but then it was all change again when Alexander was forced off with a heel injury with the second half barely four minutes old.
On came 17-year-old frontman Marquis to partner Grimes up front. And within a couple of minutes of entering the fray, a great dummy by the sub played in Grimes, whose crisply struck effort was pushed away for a corner by Andersen at full stretch.
Marquis was again involved after 57 minutes when he met Dunne's deep cross, but was unable to direct his header on target.
At this stage, The Lions were playing with a new-found impetus and when Dunne's goalbound diving header from Schofield's delivery on 62 minutes was deflected for another corner it seemed odds-on that the next goal was going to be an equaliser for Jackett's side.
But Schofield's resulting corner was cleared, play quickly swung up the other end following good work by Wright and Hughes. Hughes picked the ball up, took a couple of touches and then let fly with an unstoppable 25-yarder into the top corner.
That second goal clearly knocked the stuffing out of a Millwall side who battled gamely, but were thereafter put under pressure by a Rovers outfit that always looked capable of adding to their tally.
It took a brave block by keeper Forde to deny Lescott as he raced clear on 80 minutes and then Hughes contrived to fire wide of an empty net from six yards with the goal at his mercy as Rovers pressed forward, albeit unsuccessfully, in a bid to increase their tally.
Despite finishing the game goal-less and point-less, there was one major positive to take out of the match - the performance of youngster Marquis who showed some nice touches, good awareness and didn't seem overawed by his perhaps unexpectedly early introduction to senior football.
Bristol Rovers: Andersen, Regan, Coles, Anthony, Lescott, Wright (Pipe, 73mins), Campbell, Lines, Hughes, Kuffour (Blizzard, 82mins), Duffy (Williams). Subs not used: Evans, Elliott, Reece, Swallow.
Booking: Regan (76mins)
Scorers: Hughes (25mins, pen), Lines (63mins)
Millwall: Forde, Dunne, Barron, Fuseini, Frampton, Smith, Martin (Friend, 46mins), Abdou, Grimes, Alexander (Marquis, 49mins), Schofield. Subs not used: Sullivan, Bolder, Hughes-Mason.
Booking: Frampton (25mins), Smith (73mins), Fuseini (73mins)
Ref: Jon Moss
Att: 6,038 (away 380)