Craig Bryson hit a hat-trick as Derby County sent Millwall sliding to the foot of the Championship table with a comfortable win at The Den.
Jake Buxton headed The Rams into an early lead before Bryson took centre stage with a stunning trio of finishes before sub Mason Bennett (87mins) added a fifth.
To make matters worse, the Lions had Shane Lowry sent off for a high challenge on Will Hughes moments before Bryson's second.
The only bright spot for Millwall was a goal for debutant Martyn Waghorn, who came on with The Lions trailing 2-0 at the break and provided a glimmer of hope with a clinical strike to reduce the arrears at 3-1, but by then the damage had already been done.
Millwall went into action having won just two out of 13 home league games at The Den in 2013 but despite a bright start, within nine minutes the defensive frailties from set-plays proved costly once again. Jamie Ward's corner was punched clear by keeper David Forde but the ball fell invitingly for the Derby man to ping a cross straight back in and Buxton rose above Danny Shittu to head home.
The Lions struggled to get any attacking rhythm going with the only first-half scoring opportunity courtesy of Scott McDonald, who produced some delightful footwork to weave his way into the danger zone before despatching an effort that curled a foot wide.
That failure to defend set-pieces yet again came back to haunt the home side in first-half injury-time when, having been unable to clear their lines from a free-kick, the ball fell to Bryson some 25 yards out and he lashed the ball into the back of the net with aplomb.
Manager Steve Lomas brought on Waghorn and James Henry at half-time for Andy Keogh and Shaun Derry in a bid to spark a second-half revival.
And despite some promising exchanges straight after the restart, The Lions' were left facing a mountain to climb when Shane Lowry was shown a straight red card for a high challenge on Derby's Will Hughes.
The Rams took advantage of their numerical superiority as Bryson fired home another unstoppable shot from 30 yards and although The Lions grabbed a consolation courtesy of Waghorn, who fired past Lee Grant from 12 yards, there was to be no way back.
Derby restored their three-goal advantage when Bryson tucked home from inside the area to complete his hat-trick nine minutes from time.
Millwall's misery was complete when Rams substitute Bennett took advantage of a misplaced pass by Liam Trotter and fired an angled drive beyond the reach of the stranded Forde.
Forde, Connolly, Lowry, Shittu, Beevers, Chaplow (Trotter, 66mins), Derry (Henry, 46mins), Bailey, Woolford, Keogh (Waghorn, 46mins), McDonald. Subs not used: Bywater, Robinson, Osborne, Martin.
Bailey (23mins), Shittu (45+1min), Chaplow (45+2mins)
Derby County: Grant, Hughes, Eustace, Martin (Bennett, 77mins), Smith (Freeman, 61mins), Russell, Buxton, R.Keogh, Forsyth, Bryson, Ward (Coutts, 58mins). Subs not used: Sammon, Deeney, Davies, Jacobs.
Bookings: Martin (15mins), Smith (31mins), Bryson (52mins), Hughes (53mins), Grant (75mins)
Scorers: Buxton (9mins), Bryson (45, 57, 81mins), Bennett (87mins)
Att: 9,523 (away 667)