Theo Robinson picked the perfect time to score his first goal for Millwall as Kenny Jackett's bravehearts battled to take the derby honours in a fiesty Selhurst Park encounter.
Robinson, making only his second start for The Lions following his loan move from Huddersfield Town, kept his cool to fire home the winner from an acute angle on 53 minutes.
Although neither side could be accused of lacking effort or commitment, the frenetic pace at times saw the quality of football perhaps not reach the heights hoped for as the teams locked horns for the first time in five years.
Not that come the final whistle any one of the 4,805 Lions fans packed into the Arthur Wait Stand were concerned as they celebrated in full voice!
Millwall have enjoyed the better run of results in recent meetings against Palace and this success now means that The Eagles have failed to beat The Lions in eight of the last nine fixtures.
"It was a hard fought win," said Kenny. "We knew that because it was a derby it was going to be a battle, but after the run we've been on it is a great win and well deserved."
With Alan Dunne suspended, boss Jackett was forced to shuffle his playing pack and opted to switch Scott Barron to an unaccustomed right-back role for only the second time in his Millwall career. Darren Carter came in for his third start in a Lions shirt - ironically all away from The Den - to slot in on the left of midfield.
However, it was Palace who settled into their stride more quickly as George Burley's outfit forced four corners in the opening five minutes.
Slowly but surely The Lions started to pose an attacking threat themselves and on 11 minutes a great piece of work by Robinson saw his low cross eventually nicked off the toes of Steve Morison by Claude Davis.
The visitors chalked up a couple of decent chances with Julian Speroni comfortably saving a weak Morison shot before working a bit harder to make a fine save after Morison had controlled Tony Craig's deep free-kick and hit a thumping effort goal-bound from close range.
Robinson hooked over from a Chris Hackett corner on 21 minutes, but it was far from all Millwall as Palace too created some decent openings of their own.
Wilfried Zaha - who started like a train before running out of steam badly in the second-half - set up Pablo Counago on 23 minutes, only for the striker to fire wide from a great position.
If that miss was bad, worse was to follow 13 minutes later when teenager Zaha did all the hard work, creating time and space to fire home, but spurned the glorious opportunity to put Palace 1-0 up by curling his effort past the far post.
Eagles skipper Paddy McCarthy skied the ball high and wide from five yards after Millwall struggled to clear one of nine corners for the home side in the opening half, but McCarthy's blushes were saved by the linesman's flag.
Robinson and Morison both had half-chances that flew narrowly off target at the other end as the first 45 minutes drew to a close.
Zaha was lucky to escape a yellow card five minutes after the restart with an ill-timed, rather malicious tackle on Hackett that sent the Millwall winger flying, but the frustration on the visiting bench soon turned to cheers just three minutes later.
Goalkeeper David Forde launched a free-kick from inside his own half, Morison flicked on to Robinson, who used his pace to skim past Julian Bennett, rounded keeper Speroni and calmly fired home from the tightest of angles to spark wild celebrations from the Lions camp both on and off the field.
Having grabbed the lead, and the initiative, there was no way Millwall were going to relinquish their position in charge.
Skipper Paul Robinson and Darren Ward may have defended like lions in the heart of defence, but it was centre half turned midfielder Tamika Mkandawire who proved unbeatable as he twice made simply magnificent last-ditch tackles on Zaha as he prepared to pull the trigger in the danger zone.
Although Palace were enjoying the greater possession at this stage, it was easy to see why they have the lowest shots-on-goal ratio by any Championship team as there was no real end product to their build-up play.
Sub Neil Harris was a whisker away from showing how it should be done when, with his first touch of the ball after replacing match-winner Robinson on 79 minutes, he sent a trademark curler inches past Speroni's left-hand post.
Counago screwed an effort into the side netting at the other end as The Eagles tried to build up a head of steam as the game approached the 90 minute mark.
But the only steam they managed was that of rage when, following a tussle between Davis and Hackett on the byline, Davis appeared to leave his boot in Hackett's face, after Hackett was penalised for pulling his shirt. The Millwall man received a yellow card and the Palace defender a straight red for violent conduct.
That dismissal effectively ended any hope The Eagles had of snatching a late leveller as The Lions held on comfortably during four and a half minutes of injury-time for a deserved win to move to within two points of the Play-Offs.
Crystal Palace: Speroni, Clyne, Davis, McCarthy, Garvan, Dorman (Obika, 79mins), Cadogan (Djilali, 66mins), Zaha, Bennett, Marrow, Counago. Subs not used: Price, Andrew. Davids, N'Diaye, Gardner.
Sent off: Davis (91mins)
Millwall: Forde, Mkandawire, Craig, Abdou, Robinson, Ward, Barron, Carter (Schofield, 87mins), Morison, T.Robinson (Harris, 79mins), Hackett (Henry, 92mins). Subs not used: Mildenhall, Frampton, Marquis, Lisbie.
Bookings: Barron (56mins). Hackett (91mins)
Scorer: T.Robinson (53mins)
Att: 19,131 (away 4,805)