Chris Martin's 89th-minute header helped Norwich clinch the battle of League One's top two at Carrow Road and plunged Leeds' once seemingly certain automatic promotion prospects into doubt.
Despite leading the table by eight points at the turn of the year, a run of 15 points from 15 games since has left them clinging onto second place in the table by a single goal from charging Millwall.
While Simon Grayson's men were sliding to their nervy defeat at Norwich - who extended their lead to 11 points - the Lions were eating into a plus-seven goal difference by hammering rock-bottom Stockport 5-0.
A tense showdown between the top two had produced few clear first-half chances and a stalemate beckoned until Martin's late strike. To make matters worse for Leeds, substitute Tresor Kandol was sent off in injury time for violent conduct.
Millwall, who had blown the automatic promotion race wide open by winning at Elland Road last week, cruised to victory at the New Den with goals from Danny Swailes, Steve Morison, Dany Schofield, Jonathan Obika, and an own goal.
Charlton started the day in fourth but had to settle for a point at play-off hopefuls Huddersfield, for whom Jordan Rhodes opened the scoring before a 58th minute equaliser from the visitors' on-loan Kyel Reid.
The win moved the Terriers within three points of the top six and also enabled Swindon to leapfrog the Addicks into fourth after Charlie Austin's 16th goal of the season was enough to earn the points at Hartlepool.
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