First-half goals from Matt Smith (19mins) and Ross McCormack (41mins) secured maximum points for Leeds United as Millwall's relegation worries mounted with this defeat at Elland Road.
Sub DJ Campbell reduced the arrears with a blistering 71st-minute strike from 20 yards, but despite piling on the pressure Ian Holloway's charges just could not muster a second goal and point that their performance so deserved.
Results on the day elsewhere were kind to Millwall though, and boss Ian Holloway should take real encouragement in the way that his team played with fellow strugglers Birmingham City next up at The Den this Tuesday, themselves in a desperate scrap to get away from the drop zone.
Holloway made three changes to the team held to a 0-0 home draw by Charlton last Saturday with Mark Beevers, John Marquis and Scott McDonald replacing Shaun Williams, Simeon Jackson and Steve Morison, unable to play against his parent club.
The Lions looked crisp and inventive in the opening exchanges and Beevers, starting at left-back, got his head to Owen Garvan's corner but headed straight into the hands of keeper Jack Butland.
Ed Upson's inviting fourth-minute free-kick was deflected and heading for the bottom corner only for keeper Butland to brilliantly tip the ball away for another corner as the visitors pressed for the opening goal.
Upson, who at this stage was running the game in midfield, despatched another excellent delivery on eight minutes but on this occasion Tom Lees managed to get a touch to divert the ball away from Fred Onyedinma.
Millwall were looking comfortable and had been barely troubled by a Leeds side that were fairly anonymous as an attacking threat.
Unfortunately all that changed with 19 minutes on the clock when Connor Wickham's long throw was met by Smith, whose backward header looped over David Forde and dropped into the back of the net.
The Lions went close to levelling eight minutes before the break when Upson picked out Martyn Woolford on the right. The latter worked his way into the danger zone and hit a crisp left-foot shot that Butland did well to save.
However it was Leeds who somewhat fortuitously doubled their tally after 41 minutes. Upson embarked on a penetrative run down the flank but his pass to Marquis ricocheted upfield straight into the path of McCormack, who broke into the penalty area and somehow squeezed home from the tightest of angles.
That looked to be game over for a Lions side who have found goals hard to come by this season. But nothing could be further from the truth as Holloway's men caused their Leeds counterparts all sorts of problems in the second-half, without getting their just rewards.
Millwall came out on the front foot and a sweeping move saw McDonald spray the ball wide to the overlapping Beevers, whose rasping angled drive was held at the near post by Butland in the home goal.
At the other end the towering Smith, all 6ft 8in of him, was a whisker away from adding a third for Leeds but sent his header from Sam Byram's cross narrowly wide.
The Lions came close to pulling one back through the excellent McDonald when he looked to have tapped home, but Butland managed to smother the ball on the line to retain the two-goal advantage.
Holloway made three changes just before the hour mark, bringing on Stefan Maierhofer, Jackson and Campbell for Onyedinma, Marquis and Upson - and the move nearly proved a stroke of genius.
McDonald, the game's outstanding performer, dropped deeper back into midfield where he was involved in all things good that Millwall did.
The Lions worked tirelessly for a lifeline, and it duly came when Maierhofer chested the ball down into Campbell's path and he hit a belter from 20 yards that whistled past Butland and into the top corner. That breathed confidence and hope into Millwall's quest of trying to get something out of the game and they piled on the pressure in the final quarter of an hour.
Maierhofer's drive was blocked by the legs of keeper Butland and then in an almighty goalmouth scramble both Jackson and then Woolford had goalbound efforts blocked by desperate Leeds defending.
Garvan fired over with a free-kick from 20 yards and then McDonald too, tried his luck from distance, but slipped at the crucial moment and sliced the ball off target after weaving his way into a good position.
Five minutes of injury time failed to produce that elusive second goal for The Lions, but the team will head into Tuesday night's game against Birmingham City with renewed optimism that their battle to preserve their Championship status is not going to be given up without a fight.
Butland, Lees, Pearce, Murphy, Austin, Wickham (Hunt, 85mins), Pugh, Smith, Byram (Wootton, 90+1min), Mowait (Tonge, 83mins), McCormack. Subs not used: Cairns, Warnock, Poleon, Stewart.
Austin (74mins), Hunt (90+5mins)
Smith (19mins), McCormack (41mins)
Millwall: Forde, Dunne, Beevers, Lowry, Robinson, Upson (Campbell, 58mins), Garvan, Woolford, McDonald, Marquis (Maierhofer, 57mins), Onyedinma (Jackson, 58mins). Subs not used: Bywater, Fredericks, Abdou, Powell.
Booking: Maierhofer (68mins)
Scorer: Campbell (71mins)
Ref: S. Attwell