Two goals in 10 second-half minutes from David Prutton and Andy Hughes sunk Millwall as Leeds strengthened their Play-Off ambitions with victory at The Den.
Gillingham's 1-1 draw at Bristol Rovers coupled with Crewe's 3-1 win at home to Cheltenham leaves The Lions just four points from the drop zone with two games to go.
Saturday's Den encounter - played in front of a season's best home crowd of 13,395 - was a fiesty affair that threatened to spill over in injury-time when former Lion Peter Sweeney's antics sparked a melee that saw players from both sides trying to pull the Leeds sub away from Lewis Grabban.
Both Sweeney and Grabban were promptly booked by referee Lee Mason, who handled a potentially tricky match extremely well.
This game proved to be a carbon copy of so many other Millwall matches this season, with Kenny Jackett's side dominating the opening hour, falling behind to a sucker-punch goal and then conceding a second shortly after.
Lions boss Jackett made two changes to the side that started at Hartlepool last weekend, with Andy Frampton and Ahmet Brkovic replacing Marcus Bignot and Dave Martin respectively.
A cagey opening saw both teams probing somewhat tentatively, and it was six minutes before a shot on target was registered, with Brkovic's free-kick floating a foot wide of Casper Ankergren's post.
Brkovic then fired wide on 11 minutes after picking up Bas Savage's flick, whilst the Croatian midfielder's free-kick seven minutes later was held by Ankergren.
Tony Craig was left holding his head in horror after blazing over from six yards when another Brkovic free-kick was headed into his path by Jem Karacan.
Karacan then turned provider with a neat cross to Brkovic, the latter firing over the bar.
A slick attacking move involving Karacan, Marc Laird and Jay Simpson sliced the Leeds defence open, with Simpson's shot deflected for a corner. From the resulting set-play, the diminutive Karacan sent a powerful header inches over the bar.
Savage did well to work an opening for himself on 38 minutes before hitting a low drive straight into Ankergren's hands, whilst Simpson saw his shot saved by the busy keeper as Millwall pressed in search of the opening goal.
But they had a slice of luck seconds before the break when a Leeds attack - which was a rarity - ended with Anthony Elding firing a whisker over the bar from 16 yards.
After the break Millwall picked up where they left off and were denied an opening goal by the woodwork, with Karacan's crisp first-time shot from Brkovic's pass smacking the underside of the bar before the ball was hacked clear to safety.
Simpson then took the direct approach with a run right through the heart of the Leeds defence, only to fire over from a good position.
Boss Jackett introduced Lewis Grabban for Brkovic, but within five minutes Leeds incredibly found themselves ahead when Prutton drilled low into the bottom right hand corner with a crisply struck shot from 18 yards.
Jackett responded by bringing on Dave Martin for the tireless Ali Fuseini, but The Lions to found themselves 2-0 down shortly after when the unmarked Hughes applied the final touch to a quick break down the left.
With 10 minutes remaining it was always going to be an uphill battle, and despite trying valiantly to at least reduce the deficit, a Savage cross that flew across the face of the goal was the closest The Lions came.
Now all thoughts turn to next Saturday, when Carlisle visit The Den needing victory to secure the second automatic place, whilst a win for Millwall will ensure our safety irrespective of any other results amongst the other League One basement boys.

Millwall: Evans, Senda (Bignot, 73mins), Frampton, Fuseini (Martin, 74mins), Robinson, Craig, Brkovic (Grabban, 65mins), Laird, Karacan, Savage, Simpson. Subs not used: Edwards, Harris.
Bookings: Brkovic (14mins), Grabban (90mins)

Leeds United: Ankergren, Richardson, Huntington, Prutton, Howson, Sheehan, Michalik, Kilkenny, Freedman, Elding (Hughes, 72mins), Johnson (Sweeney, 90mins). Subs not used: Marques, Lucas.
Bookings: Michalik (13mins), Sweeney (90mins)
Scorers: Prutton (70mins), Hughes (79mins)

Ref: Lee Mason
Att: 13,395 (away 1,892)