Darren Byfield kept his cool to convert a 79th-minute penalty as Millwall came from behind to stun table-toppers Oldham with a smash-and-grab raid at Boundary Park.
It was a happy return to Lancashire for Lions boss Willie Donachie, who was warmly applauded before the match by Latics fans who fondly remembered the Scot for his time at the club as a player and then right-hand man to Joe Royle.
But those same supporters must have wished that the same generosity was not extended by their players, who carved out a 1-0 advantage and looked to be comfortably on their way to three points by the hour-mark courtesy of Paul Warne's 54th-minute glancing header.
However, all that changed when Donachie made a double substitution replacing Neil Harris and Tom Brighton with Poul Hubertz and Marvin Williams.
The duo had been on the field for barely 20 seconds when Hubertz flicked on to Williams who found Marvin Elliott. He in turn threaded the ball through to Byfield and the striker's neat pass found Williams, with the young sub sliding home.
That goal sparked Millwall into action and when Stefan Stam handled the ball 11 minutes from time, up stepped Byfield to convert the resulting penalty for his 12th goal of the campaign.
Last week a double substituion by Donachie paid off handsomely against Chesterfield, but The Lions boss was forced to make an early change after 21 minutes when Alan Dunne was forced off injured.
It proved to be a disappointing return to the first team for Dunney, who was somewhat harshly booked on nine minutes for a tackle on Chris Taylor and then hobbled after bravely blocking the ball in a 50-50 challenge.
Chris Hackett came on for the unfortunate midfielder, but on a bobbly pitch littered with divots. neither side really got into their stride in a dour first-half.
Scoring chances were limited in the with Tom Brighton sending a header narrowly wide for The Lions with their only noteworthy effort.
At the other end Danny Senda's hesitency on the ball enabled Warne to nip in and set Chris Porter clear on goal, but the striker snatched at his shot and flicked the ball straight into the hands of grateful visiting keeper Lenny Pidgeley.
Warne tried his luck from 25-yards with a piledriver that flashed a foot over the bar, but that was the sum total of goalmouth action in a drab first 45 minutes.
Thankfully the match improved as a spectacle after the break, although not in the way that Millwall had anticipated when Neal Eardley's deep cross caught the visiting defence square leaving Warne space to squeeze a header home with Pidgeley rooted to the spot.
The Lions responded immediately and the introduction of Williams and Hubertz was a move that paid off handsomely with the two subs involved in the equalising goal on 61 minutes.
Donachie's charges could have forged the lead 10 minutes later when Byfield had time and space to meet Hackett's teasing cross, but he headed high and wide from eight yards.
However when handed - quite literally - the opportunity to fire Millwall ahead from the penalty spot with 11 minutes remaining, Byfield made no mistake with a clinical spot-kick that sent keeper Les Pogliacomi the wrong way.
Dave Brammer was denied a third by the fingertips of Pogliacomi, who somehow stretched enough to tip the midfielder's curling free-kick away as it headed for the top corner.
Oldham had no option other than to go for broke as they desperately tried to claw their way back. and contrived to produce arguably the miss of the season when Gary McDonald broke clean through and with the goal at his mercy, inexplicably passed the ball to no-one just four yards out.
The howls of derision from the travelling fans behind the goal was met by groans of disbelief from the Boundary Park faithful.
Other than a low drive from Taylor that Pidgeley did well to save low to his left, McDonald's miss seemed to knock the stuffing out of the hosts and provide that extra bit of belief Millwall needed to see them through an agonising five minutes of injury time to hold on for a superb win.

Oldham Athletic: Les Pogliacomi, Neal Eardley, Will Haining (Mike Pearson, 85mins), Stefan Stam, Paul Edwards (Kelvin Lomax, 77mins), Andy Liddell (Chris Hall, 77mins), Craig Rocastle, Gary McDonald, Chris Taylor, Paul Warne, Chris Porter. Subs not used: Ryan Smith, Moussa Dabo.
Bookings: Rocastle (63mins), Haining (82mins), Eardley (83mins)
Scorer: Warne (54mins)

Millwall: Lenny Pidgeley, Danny Senda, Tony Craig, Marvin Elliott, Mark Phillips, Richard Shaw, Tom Brighton (Marvin Williams, 60mins), Dave Brammer, Neil Harris (Poul Hubertz, 60mins), Darren Byfield, Alan Dunne (Chris Hackett, 21mins). Subs not used: Chris Day, Ali Fuseini.
Bookings: Dunne (10mins), Byfield (42mins), Brammer (44mins), Hubertz (63mins)
Scorers: Williams (61mins), Byfield (79mins, pen)

Ref: S. Bratt
Att: 6,181 (Away 285)