James Henry bagged the first hat-trick of his career as The Lions produced a five-star display to trounce Tranmere Rovers.
Kenny Jackett's men roared into a 4-0 lead after just 28 minutes courtesy of Henry (4 and 27mins), Andy Frampton (8mins) and Steve Morison (22mins), with Henry scoring his third - and Millwall's fifth - five minutes from time.
To compound a thoroughly miserable afternoon for the visitors, assistant manager Jason McAteer was sent off after 80 minutes, and was followed by Rovers defender Marlon Broomes five minutes later for a second bookable offence.
Lions boss Jackett made four changes to his starting line-up, two of which were enforced with defender Darren Ward and midfielder Ali Fuseini picking up knee injuries on Friday.
Tony Craig and Marc Laird came back into the fold, along with Scott Barron and Gary Alexander for Alan Dunne and Neil Harris, who both dropped to the bench.
The Lions started this game as the lowest scorers in the division and in dire need of some goals - and a win - to kick-start the campaign.
And Jackett's men took full advantage of a truly abject Rovers display to record Millwall's best home win since the Second Division title-clinching 5-0 hammering of Oldham Athletic in May 2001.
Millwall came flying out of the traps and took just four minutes to break the deadlock when Henry's free-kick from 18 yards slipped through keeper Luke Daniels' hands.
The Lions doubled their tally on eight minutes courtesy of Frampton's close range effort. Henry's corner from the left was half-cleared, Laird did well to head the ball back to Morison in the danger zone and his great chipped delivery was flicked on by Alexander to Frampton, who made it 2-0 with a towering header.
Rovers' rearguard was rocking and referee Mr Scott reached for his yellow card for a second time on 14 minutes, with Broomes following Ian Goodison (3mins) into the official's book for slicing down Alexander as he threatened to break clear from Dave Martin's quick throw-in on the left.
Henry dragged an effort wide on 15 minutes before Millwall further added to their tally eight minutes later. Henry was again involved with an inviting delivery from the right that Morsion glanced past hapless keeper Daniels.
The home side showed no mercy though, and didn't have to wait much longer to score once more. Craig played the ball through to Henry, and he ran straight at - and through - the visiting defence before despatching a clinical finish into the bottom left-hand corner.
Alexander twice sent headers narrowly off-target and then hit a 22-yarder that unfortunate keeper Daniels held at the second attempt as Millwall finished the half in total control.
As so often happens when one team has established such a commanding lead, the second-half proved to be fairly quiet in terms of goalmouth excitement.
Tranmere could not have played any worse than their first-half showing, and indeed their performance did pick up a bit.
However, the damage had already been done and despite a couple of long-range efforts from John Welsh and John Curren, Lions keeper David Forde had a quiet afternoon.
At the other end Jimmy Abdou saw his header flash over the bar and Alexander was denied by the keeper as Millwall picked up a head of steam again.
But it was Tranmere's assistant maanger McAteer who verbally let off steam once too often for the fourth official's liking on 80 minutes, and was promptly sent to the stands.
Five minutes later it was Rovers' midfielder Broomes who was seeing red, this time after picking up a second booking for a foul on Morison.
Ten-man Rovers' misery was complete when Henry stepped up to take the resulting free-kick and hit a low shot into the bottom left corner that dribbled almost apologetically over the line to wrap up victory.

Millwall: Forde, Smith, Barron, Abdou, Craig, Frampton, Martin (Schofield, 68mins), Laird, Alexander, Morison, Henry (Hackett, 86mins). Subs not used: Sullivan, Dunne, Harris, Bolder, Price.
Booking: Martin (65mins)
Scorers: Henry (4, 27, 85mins), Frampton (8mins), Morison (22mins)

Tranmere Rovers: Daniels, Logan, Cresswell, Goodison, Shuker, Broomes, Thomas-Moore (Taylor, 85mins), Ricketts (Curren, 66mins), McLaren, Welsh, Carole (Mahon, 60mins). Subs not used: Collister, Bain, Barnett, Edds, Mahon.
Bookings: Goodison (3mins), Broomes (14mins), Logan (38mins), Cresswell (90+3mins)
Sent off: Broomes (85mins)

Ref: G. Scott
Att: 8,046 (away 224)