Full-time score from The Den
Millwall handed manager Kenny Jackett the perfect tonic as goals from Liam Feeney and Andy Keogh stretched The Lions' unbeaten run to nine games.
Boss Jackett was absent through illness, but under the guidance of right-hand man Joe Gallen, The Lions really dug in and produced the first back-to-back home wins since April.
There was a hint of controversy about Feeney's 33rd-minute opener, with the linesman flagging for offside, but assistant boss Gallen said: "It was excellent interplay for our first goal and I was just admiring it when I saw the flag and thought that once the referee makes a decision, he rarely changes it.
"I didn't have a very good view from the dug-out, but it was a dominant performance in the first half and we deserved to be at least one goal up.
It took us 10 minutes to steady ourselves after conceding the equaliser, but then we did well and of course went on to win the game.
Kenny picked the team and we discussed the tactics, so he was here but not here!
Nine games unbeaten is a good achievement, but the real achievement would be to stay in the top 10 and go on from there."
With top scorer Darius Henderson and James Henry both ruled out with hamstring injuries sustained in the midweek draw at Watford, Andy Keogh and Feeney returned to an otherwise unchanged starting line-up.
Playing against an in-form Derby team that had only lost one of their previous eight games going into this clash, on paper this looked as if it had all the makings of a cracker.
However whilst there was plenty of effort and endeavour throughout, the match itself was at times a pretty bitty affair.
Liam Trotter stung the hands of Derby keeper Adam Legzdins in the third minute and then Keogh's low cross just evaded the touch of Chris Wood as Millwall produced a couple of early chances.
But after a relatively quiet opening half hour, the game sprung into life. A fine passage of attacking play saw Keogh feed Wood, who in turn played a delightful ball through to Shane Lowry on the flank. The left-back whipped in a low cross that looked to have missed everyone in the goalmouth until up popped Feeney at the back post to lash the ball into the bottom corner with a great finish.
Feeney's joy appeared to be short-lived as referee Darren Drysdale, went over to the assistant referee, who had already raised his flag prior to the goal as Keogh was in an offside position.
After a lengthy consultation, the referee, indicated that Keogh had not been 'active' and as Feeney was clearly onside when he scored, the goal stood.
The Rams tried to respond and went close to equalising seconds before the break when skipper Richard Keogh tried his luck with a spectacular effort from 35 yards that fizzed narrowly over.
Millwall were forced to make a change in the second of three minutes of injury-time when Chris Taylor was forced off, to be replaced by Scott Malone, with a back strain.
The Lions could have doubled their tally within 90 seconds of the restart only for an excellent tackle by John Brayford to avert the danger as Keogh was about to pull the trigger.
But just seven minutes later, it was Derby who were celebrating thanks to a pearler of an equaliser from Will Hughes.
Picking up the ball some 30 yards out, Hughes took a couple of strides forward and then unleashed a piledriver from the edge of the area that flew past the outstretched hands of David Forde and into the top corner.
Derby were spurred on by this and for a 10-15 minute spell it looked as if it would be the visitors who might push on and grab a second goal.
But with The backline holding firm, The Lions weathered the storm and began to work their way back into the game.
Chris Wood was denied by a clearance off the line by Richard Keogh. Adam Smith then fired over the bar following a mazy run before Keogh was thwarted by a great tackle from James O'Connor as he again worked his way into a good position.
However, the front man was not to be denied and moments later grabbed his second goal in three games with a delightful curling effort that floated past Legzdins into the top right corner.
With less than quarter of an hour remaining, time - or rather a lack of it - was of the essence for Derby as they laid seige to the home goal.
But credit to The Lions who defended admirably as a team and ran the clock down to secure another three points to move up to 10th spot - just four off the Play-Offs.
Millwall: Feeney (33mins), Keogh (74mins)Scorers:
Forde, A.Smith, Lowry, Abdou, Shittu, Beevers, Feeney, Trotter, Keogh, Wood, C.Taylor (Malone, 45+2mins). Subs not used: M.Taylor, J.Smith, Osborne, N'Guessan, Batt, Wright.
Bryson (12mins), Hendrick (26mins), Robinson 87mins)
Legzdins, Brayford, Roberts, Coutts, Robinson, Sammon (Jacobs, 80mins), O'Connor, Keogh, Bryson, Hughes, Hendrick. Subs not used: Deeney, Buxton, Tyson, Freeman, Davies, O'Brien.
D.Drysdale (change to G.Salisbury)
Att:10,392 (away 661)