Aiden O'Brien's goal inflicted Championship leaders Leeds' first defeat of the season as Millwall won 1-0 at The Den.
The Lions controlled the contest from start to finish, but for so long it looked set to be one of those afternoons where a catalogue of chances would be wasted, before they eventually broke through after 73 minutes.
Leeds were horribly off-colour at The Den having reached the division's summit earlier in the week, and were fortunate not to be on the wrong end of an emphatic result.
Fred Onyedinma lined up for Millwall in place of the suspended Lee Gregory, while Leeds defender Conor Shaughnessy made just his second league start amid a raucous atmosphere.
Millwall thought they had gone ahead in the seventh minute when Steve Morison put in a rebound after Felix Wiedwald had fumbled Conor McLaughlin's shot, but the linesman raised his flag for offside.
The Lions began superbly and it took some good defending from Pontus Jansson to prevent Morison's cut-back from reaching Onyedinma in front of goal.
Despite their dominance, the final ball was proving to be an issue for Neil Harris' side, while Jed Wallace's strike just after the half-hour mark was also pretty wayward.
Still the home side pressed, with Shaun Williams' long-range effort, after a free-kick was teed up for him, being deflected wide with Wiedwald looking worried.
The Leeds goalkeeper continued to be kept busy before half-time, as he first scrambled across to keep out Morison's header before pushing another Williams strike over the crossbar.
The second half began with more of the same, as Wiedwald was forced to push Wallace's deflected cross behind, before the German kept out Shaun Hutchinson's effort with his legs.
The one-way traffic continued and Millwall came closer still after 59 minutes as Wallace sent a good effort from the edge of the area crashing against the post, with Wiedwald beaten this time.
The home fans were starting to despair at the number of missed chances, as Wallace's cross reached Morison at the far post, with the one-time Leeds striker denied by Wiedwald.
But the breakthrough finally came with 17 minutes left as the ball broke for O'Brien to tap in after Onyedinma looked to have been up-ended in the area.
George Saville failed to make the game safe as he somehow blazed over late on, but this did not prove costly for the victorious hosts.