This may have been Derby's first home defeat in ten games but above all it was another lacklustre display that leaves them winless in five.
Where that next win will come from isn't clear because displays like this offer little in the way of confidence, a slightly improved second-half display coming after another awful first 45 - a familiar theme in recent weeks.
Millwall produced a fine defensive display, with former Ram Alex Pearce excellent at the heart of the back four, both he and boss Gary Rowett able to leave their former stomping ground with their heads held high.
But Derby shouldn't have let them have that luxury, a performance lacking in all areas leaving their fans frustrated once again and questions being asked as to just where the Rams go from here as they wait for January to come and with it the arrival of Wayne Rooney and, many will hope, some other new faces too.
Millwall soaked up early possession from the Rams and then nearly hit the hosts on the counter, Jon Dadi Bodvarsson's through ball finding Jed Wallace but his low shot was easily gathered by Ben Hamer.
A dull game then got its opening goal on 25 minutes. A ball through the middle was flicked on by Bodvarsson to release Tom Bradshaw and he finished well into the top corner of the net to give the Lions a lead they arguably deserved.
The Rams were struggling to make anything happen, much to the frustration of the home fans, Duane Holmes with their first effort of note on the half hour which flew high and wide.
But that would be the best they'd have to offer from a very negative first-half display that lacked quality, movement, ability and passion throughout.
The second-half started better, Tom Lawrence's break down the left ending with a square ball which Martyn Waghorn skewed over the bar when in a good position six yards out.
Chances were still few and far between, Waghorn striking from 25 yards on 65 minutes but seeing Bartosz Bialkowski push his shot away, then the Lions keeper turned Jayden Bogle's cross away from danger as it looked like it could drop into the net.
Waghorn then shot wide from a Curtis Davies cross on 76 as the Rams continued to probe for a goal, then Bogle's low cross was nearly turned into his own net by Shaun Williams but Bialkowski got down well to turn the ball past the post.
But the Rams would have little else to offer and it was hard to argue that Millwall didn't deserve their win.
Derby: Hamer, Forsyth (Jozefzoon 81), Waghorn, Lawrence, Evans, Martin, Holmes (Whittaker 88), Lowe, Davies (c), Bogle, Knight (Dowell 74)
Subs not used: Roos (GK), Wisdom, Bielik, Malone
Millwall: Bialkowski, M Wallace, Hutchinson, Cooper, Williams, J Wallace, Bradshaw (O'Brien 81), Romeo, Pearce (c), Molumby, Bodvarsson (Thompson 67, Smith 88)
Subs not used: Steele (GK), Ferguson, Mahoney, Skalak
Ref: Chris Kavanagh