Two late goals from David McGoldrick, after Millwall had fought back from 1-0 down, secured Sheffield United's first victory at The Den since 2010.
Chris Wilder's side appeared destined for defeat when first Jake Cooper and then Lee Gregory pounced following Billy Sharp's opener for the visitors.
Having missed a penalty earlier, Sharp stepped aside when Mark Duffy was fouled inside the area during the closing stages. Instead, it was McGoldrick who stepped-up, slotted home before claiming a last gasp winner.
Dean Henderson 6
Although the scoreline would suggest otherwise, United's goalkeeper had little to do at The Den. He was left horribly exposed for Millwall's second.
Chris Basham 7
Always works hard but the defender has become increasingly creative in recent weeks. The trend continued here with an early pass to Billy Sharp nearly creating a goal before his influence waned.
John Egan 7
Never afraid to put his head in where it hurts, illustrated by the fact he finished the first-half with a heavily bandaged forehead, the defender showcased some fine pieces of control too.
Jack O'Connell 7
His battle with Steve Morison, the Millwall centre-forward, was a no-holds-barred affair. Was often called for holding the veteran forward but, with Morison backing in, what else could be do?
Enda Stevens 7
Always a threat going forward, the Republic of Ireland defender seems to have grown in confidence since making his full international debut recently, hence his improved work at the back.
Kieron Freeman 7
The fact he spent most of the afternoon in the opposition half spoke volumes about both the dynamic of the game until two defensive lapses left United in a hole.
Oliver Norwood 7
A delight to watch, the on-loan midfielder, whose move will become permanent in January, not only plays the right pass but then points and tells the recipitent exactly what to do with it.
John Fleck 7
Got the better of Ryan Leonard for the majority of the afternoon before his United team mate, on loan at Millwall, found room to provide the assist for Lee Gregory's goal.
Mark Duffy 8
The cross, after a fine interchange with McGoldrick, that created Billy Sharp's first-half strike simply begged to be turned home. He never stops trying to create which proved crucial during the closing stages. My man of the match.
Billy Sharp 7
Worked his socks off and ensured the opposition players could never settle on the ball. Will be desperately disappointed to have missed his first-half penalty but made up for it with a well-taken goal.
David McGoldrick 8
His movement and touch have brought an extra dimension to United's attack but stayed on the periphery of this game until commanding centre-stage when it mattered most.
Substitutes: Marvin Johnson (for Stevens, 74), Richard Stearman (for Duffy, 89), Leon Clarke (for McGoldrick, 90). Not used: Simon Moore, Conor Washington, Paul Coutts, John Lundstram.