The pantomime season was in full flow at the Den in an extraordinary match that produced 10 bookings, five goals, two red cards and more drama than all the Christmas soap specials wrapped into one.
Lee Hughes proved to be the villain of the piece with a hat-trick to clinch three points for an Oldham side that, like Millwall, finished with 10 men.
Running Hughes a close second in the booing stakes was referee Kevin Friend, who frustrated both sets of players with some, at times, infuriatingly inconsistent decisions.
After a quiet opening the game sprung into life after 31 minutes when Hughes got just enough of the ball to steer it past Lenny Pidgeley. Despite his elaborate and lengthy celebrations, referee Friend took no action and some 50 seconds later the game re-started.
Jay Simpson, booked for an innocuous challenge on 36 minutes, latched onto an incisive Paul Robinson through ball and slammed The Lions level after 38 minutes.
Yet when the young striker celebrated with the home fans, Mr Friend brandished a second yellow card and the stunned teenager left the field in tears unable to take any further part in proceedings.
Millwall's 10 men responded superbly and in first-half injury time goal-machine Zak Whitbread was perfectly placed to steer home a Dave Brammer free-kick for his third goal in seven games.
But back came Oldham after the break and Hughes was a whisker away from hauling the visitors level on 64 minutes with a bullet header from Ryan Bertrand's cross that flashed a foot wide.
A sweeping Millwall move on 69 minutes involving Danny Senda, Ali Fuseini and Will Hoskins nearly created an opening for Gary Alexander, but his effort was diverted for a corner.
Four minutes later Oldham were handed a perfect opportunity to get back into the game when referee Friend awarded John Sheridan's side a penalty. What for? Who knows. Certainly no Oldham players appealed for a foul, handball or possible infringement. But not one to look a gift horse in the mouth, Hughes promptly smacked home his second goal, insisted on repeating his fanciful celebrations and again avoided a yellow card. Not so Lenny Pidgeley, who was booked before play had resumed. Answers on a postcard please.
Hughes bagged his third after 80 minutes with a hooked close-range effort into the top corner and whilst the striker again avoided any form of punishment for his lengthy celebrations, team-mate Neal Eardley was shown a red card for his second booking. Answers, again, on a postcard please.
Despite a further flurry of bookings and Whitbread so nearly grabbing a 94th-minute equaliser with a powerful header from Brammer's freekick, there was sadly to be no way back for the battling Lions.

Millwall: Pidgeley, Senda, Bignot, Brammer, Robinson, Whitbread, Fuseini (Akinfenwa, 80mins), Hodge, Alexander, Hoskins, Simpson. Subs not used: Day, Barron, Bakayogo, Shaw.
Bookings: Simpson (36mins), Fuseini (42mins), Alexander (67mins), Pidgeley (74mins), Bignot (90+4mins), Hoskins (90+4mins)
Sending off: Simpson (38mins)
Scorers: Simpson (38mins), Whitbread (45mins)

Oldham Athletic: Crossley, Eardley, Trotman, Stam, Bertrand, Taylor, McDonald, Kilkenny, Allott, Hughes (Hazell, 82mins), Davies. Subs not used: Bell, Smalley, Kalala, Thompson.
Bookings: Eardley (43mins), Kilkenny (71mins)
Sending off: (Eardley,80mins)
Scorer: Hughes (31, 73pen, 80mins)

Ref: Kevin Friend
Att: 8,033 (away 234)