Millwall striker Neil Harris went past Teddy Sheringham's club record of 93 league goals as they routed Rotherham.
He scored after 16 minutes when Paul Robinson's header was parried by Rotherham keeper Neil Cutler.
Chris Zebroski added the second after 26 minutes and Darren Byfield headed a third before the interval.
Rotherham's Justin Cochrane was sent off for a second bookable offence before Byfield added a stunning fourth from 35 yards in the last minute.
Millwall: Pidgeley, Senda, Robinson, Shaw, Craig, Dunne, Ardley (Morris 68), Williams (Brighton 60), Zebroski (May 78), Harris, Byfield.
Subs Not Used: Day, Hubertz.
Booked: Dunne, Byfield.
Goals: Harris 16, Zebroski 26, Byfield 39, 90.
Rotherham: Cutler, Wiseman, Worrell, Sharps, Brogan, Partridge (Diagouraga 84), Cochrane, Bopp, Woods, Facey (O'Grady 55), Henderson.
Subs Not Used: Montgomery, Newsham, King.
Sent Off: Cochrane (82).
Booked: Cochrane, Bopp.
Referee: K Hill (Hertfordshire).