Last time these sides met, it was more than flash footwork and fancy finishing which stole the headlines, after former Lions goalkeeper Liam Roberts saw red for a rash challenge on Palace striker Jean Phillipe-Mateta.
The fallout in the ground and on social media since stoked the flames of an already inflamed rivalry, making their meeting in the Carabao Cup Third Round an immediate standout.
To add further hostility to the occasion, Millwall academy graduate Romain Esse was handed his first start of the season for Palace, who he joined from the Lions for £14.5 million in January.
He has so far struggled to cement himself in Oliver Glasner’s thoughts, with Tuesday’s showing offering little to change that after the young star was taken off at half-time, replaced by deadline day signing Christantus Uche.
When Eberechi Eze departed for Arsenal last month, Glasner was clear that, in the short term, Esse could not replace the England international. “Not now, honestly, not now,” the Austrian said at the time.
A Daniel Muñoz cross after 15 minutes deflected off of Daniel Kelly before landing at the feet of Esse in the box.
Not expecting to receive the ball, his touch was heavy, and he struggled to gain control of the ball before the chance petered out.
Just a minute later, the England U21 international directed another effort goalward, but his tame attempt from outside the box rolled into the expectant arms of Steven Benda.
An encouraging start for Millwall was dealt an early blow when Kelly had to be replaced in the 23rd minute after sustaining an injury, with loanee Thierno Ballo replacing him.
The Lions battled on, seemingly unaffected, however, and continued to ask plenty of questions of the Palace defence in an otherwise even first half, where the visitors edged the chances.
There was no chance better than when Ballo played Camiel Neghli through one-on-one with Benítez, though the Algerian placed his effort wide of the far post.
The second half brought with it a different feel, one of growing Palace control, even if chances did not immediately follow.
But the persistence of Oliver Glasner’s side was rewarded and, in the 72nd minute, Richards fired the Eagles into the lead, and into the driving seat to reach the fourth round.
A corner was headed on by Uche to Mateta, who held the ball up excellently before a scramble saw it fall for Richards, with the American international making no mistake as he rocketed his effort past Benda.
The setback did not see Millwall’s spirit falter, and the Lions continued to press for an equaliser throughout the remainder of the game.
It looked as though Millwall had exhausted their chances and, with time rapidly running out, it was going to take a moment of brilliance for the Lions to salvage the tie.
That moment arrived. 19-year-old Jack Howland’s corner in the 91st minute was headed across goal by Leonard, an effort which beat Benítez as it nestled into the far side to square the game.
Mateta had a chance to win it for Palace late on, but, faced with a near-empty net, the Frenchman failed to keep his effort on target after Muñoz had squared it to him.
The battle was over, but the war raged on as both sides prepared for the penalty shootout, with nothing to split the foes after 90 minutes.
Mateta stepped up first and, despite Benda getting a hand to it, his effort nestled into the top right corner.
Tristan Crama was up next, and Benítez got down quickly to his right to deny the Millwall skipper.
A composed finish from Chris Richards into the bottom left sent Benda the wrong way as Palace extended their advantage.
Benítez guessed right for Wes Harding’s attempt, but was unable to keep the effort out of the middle of the left-hand side.
Justin Devenny dispatched an excellent spot-kick into the top right corner, with Benda once again guessing wrong, not that it would have mattered.
Millwall’s hero of the moment, Leonard, converted once more to make it 3-2 in the shootout after three penalties each.
Daichi Kamada thundered his attempt into the bottom right corner to pile the pressure on Millwall, who knew that they had to score to stay alive in the tie.
That responsibility fell to Aidomo Emakhu, whose attempt down the middle of the goal was comfortably held by Benítez to send Palace into the hat for the fourth round.