Super sub Ricardo Fuller stepped off the bench to grab his sixth goal of the season - and what a priceless one at that - as Millwall boosted their Championship survival hopes with a superb 1-0 win at the City Ground.
There were just seven minutes remaining when Fuller, a 71st minute replacement for Magaye Gueye, latched onto Stephen McLaughlin's poor header back and showed ice-cool composure as he rounded keeper Dorius de Vries before slotting the ball into an empty net.
The goal capped an excellent, controlled and disciplined display by Ian Holloway's side who built on Tuesday night's 0-0 draw against Reading with a second successive clean sheet and three crucial points.
From back to front, The Lions looked strong, hungry and determined, with the exquisite flair of Diego Fabbrini a key factor in this win. The Watford loanee was at the heart of so much of Millwall's positive play and had the away fans chanting his name long after the final whistle in appreciation.
Millwall, showing three changes to the team that started against Reading - Alan Dunne, Mark Beevers and Lee Martin in for Sid Nelson, Dan Harding and Lee Gregory - were first to threaten when a deep delivery by Beevers was cleared away.
At the other end Dunne did well to block a dangerous cross from Michail Antonio and then central defensive partner Jos Hooiveld denied Henri Lansbury with another brave block as the home side pressed for an early opener.
The Lions were forced to re-shuffle on the quarter hour mark when Martin went off with a rib injury and Ed Upson came on, and as the minutes ticked by so Millwall grew in confidence.
A little spell of pressure saw Gueye blast a shot wide of the Forest goal, before defender Hooiveld charged down on goal and unleashed a 25-yard effort that flew narrowly off target.
Millwall looked to have made the break through a couple of minutes before half-time when Beevers, who performed admirably at left-back, powered a header from Upson's free-kick towards the bottom corner. Forest keeper de Vries flung himself across goal and clawed the ball away as it arrowed towards the bottom corner.
Forest had a couple of half-chances before the break with Robert Tesche and then Lansbury both firing efforts in on goal that were cleared by a stoic Millwall rearguard action.
Stuart Pearce's men started the second-half on the front foot and midfielder Tesche smashed a speculative 30-yard shot against the crossbar on 49 minutes.
It took the brilliance of Lions keeper David Forde to deny Britt Assombalonga after 54 minutes, getting a hand to the striker's point-blank header and clawing the ball away from under the bar.
Forde was called into action again, this time saving from Antonio after the Forest man weaved past a handful of defenders and got a shot in on goal.
Stefan Maierhofer twice had decent chances in front of goal, first sending a dipping shot over the bar from Shaun Williams' lofted pass and then heading wide seconds before he was replaced by Gregory on 61 minutes.
With the delightful close control of Fabbrini causing panic in the Forest defence every time he was in possession, The Lions looked increasingly like they had the key to opening the Forest defensive door.
And so it proved when, with just seven minutes remaining, Fuller latched onto McLaughlin's weak header, used all his experience and nous to wrong-foot the keeper, round him and roll the ball home from four yards.
It was a big moment in the game, and come May, could just prove to be one of the biggest moments in Millwall's season.
De Vries, Wilson, Assombalonga, Lansbury, Kane, Antonio, Hobbs, Burke (Fryatt, 60mins), McLaughlin, Tesche (Paterson, 70mins), Osborn. Subs not used: Darlow, Lichaj, Fryatt, Fox, Veldwijk, Lascelles.
Antonio (31mins), Tesche (52mins)
Millwall: Forde, Cummings, Beevers, Dunne, Hooiveld, Abdou, Williams, Martin (Upson, 16mins), Gueye (Fuller, 72mins), Maierhofer (Gregory, 61mins), Fabbrini. Subs not used: King, Webster, O'Brien, Powell.
Bookings: Upson (33mins), Williams (80mins)
Scorer: Fuller (83mins)
Ref: M Heywood
Att: 23,018 (away 682)