Millwall were predictably a threat at set pieces and the giant Jake Cooper proved a big problem, the centre-back providing a headed assist from a free-kick for Japhet Tanganga to net the only goal of the game five minutes before the break.
Leeds huffed and puffed and joy turned to dismay midway through the second half when Joel Piroe thought he had drawn his side level, only to be greeted by an offside flag. Whites boss Daniel Farke then threw on an array of forwards but only the frame of the goal denied Millwall a second goal from a set piece as Mateo Joseph’s attempts to clear a Cooper header bounced back off the post.
Leeds needed to win to climb back into the division's automatic promotion places after Tuesday night's victory for Sheffield United at Bristol City but the Whites now remain third, two points behind the Blades and now four pints behind leaders Sunderland.
Victory for Millwall also sent the upwardly mobile Lions into fifth and now just four points behind Leeds who are only three points ahead of fourth-placed Burnley who also have a game in hand.
Graham Smyth, the YEP’s chief football writer, hands out the scores from a night to forget at The Den.

1. Illan Meslier
7 - Could do little with the goal, had nothing else to do in the game other than pass the ball or occasionally clear. Photo: Alex Davidson

2. Jayden Bogle
5 - One dangerous cross aside he was unable to provide in the final third. Some poor touches that cost him and Leeds momentum or position. Photo: Naomi Baker

3. Joe Rodon
6 - Couldn't stop Cooper from winning the first headers but who ever does? Battled. Some nice passing forward. Photo: Zac Goodwin

4. Pascal Struijk
6 - Couldn't anticipate or react quickly enough to stop Tanganga's effort but that's nitpicking given how quickly the situation developed. Battled well with Coburn. Photo: Ryan Hiscott

5. Junior Firpo
6 - A couple of nice moments going forward but the link-up play on the left rarely unlocked Millwall's defence. Booked for a rash lunge. Photo: Lewis Storey

6. Ao Tanaka
6 - Some good stuff to keep the ball but like many of his colleagues he didn't find any solutions to what Millwall threw up once they had a lead. Photo: Alex Davidson