Caretaker player-boss Richard Shaw suffered his first defeat at Millwall boss as unbeaten Leeds surged into the play-off places with an emphatic win.
David Prutton put Leeds ahead with a 20-yard effort and after the break Jermaine Beckford fired in a second.
Jonathan Douglas was on hand to convert Ian Westlake's corner and added a 20-yard free-kick to make it 4-0.
Will Hoskins fired home and debutant Ahmet Brkovic headed in Jamie O'Hara's cross for late Millwall consolations.
Leeds: Ankergren, Richardson, Marques, Heath, Clapham, Prutton, Douglas, Westlake, Carole (Weston 78), Kandol, Beckford (Da Costa 90).
Subs Not Used: Lucas, Huntington, Andrews.
Goals: Prutton 37, Beckford 53, Douglas 57, 60.
Millwall: Pidgeley, Senda, Robinson, Shaw, Frampton, Brkovic, Fuseini (Simpson 62), Dunne, O'Hara, Alexander, Hoskins.
Subs Not Used: Day, Whitbread, Harris, Barron.
Booked: O'Hara, Brkovic.
Goals: Hoskins 65, Brkovic 76.
Ref: Mark Halsey (Lancashire).