With both high-flying Leeds and Oldham losing before kick-off at the Den, Millwall wasted a great opportunity to distance themselves from the chasing pack.
In-form Lewis Grabban should have handed the hosts the lead on six minutes, but the 20-year-old blasted across former Lions keeper Willy Gueret and wide.
The visitors snatched the lead on eight minutes when Sean O'Hanlon lashed home from close range after the Lions failed to clear Peter Leven's dangerous in-swinging corner.
Five bookings were dished out during a spate of late and fiery tackles as the hosts began to dominate.
Then against the run of play, debutant Luke Chadwick bundled his way to the byline before finding Mark Wright ten yards out.
With the whole goal to aim at, the winger was denied by a top drawer save by the legs of David Forde.
With first-half injury-time ticking away, the instrumental Chadwick fed Sam Baldock who beat the offside trap to round Forde and side-foot home into the empty net.
Lions skipper Paul Robinson put the game beyond doubt for his own side when he inadvertently put the Dons 3-0 up on 62 minutes.
Whilst shadowing the ball back to his keeper Forde and under pressure from persistent Baldock, the defender toe-poked into his own net.
Former Manchester United midfielder Chadwick had orchestrated the Dons and earned an ovation from the 566 away fans ten minutes from time.
With full time approaching, Baldock snatched his second of the afternoon and the easiest of his life.
Wright's shot took a wicked deflection that looped over back-peddling Forde, who did well to tap onto the bar, but the ball came back into play for Baldock to tap home from less than a yard.