For the third straight game Leeds ended a contest with 10 men, Liam Cooper following in the footsteps of team-mates Samuel Saiz and Eunan O’Kane in being handed a red card.
Cooper was given his marching orders shortly before half-time for a late challenge on George Saville, which led to a touchline melee that saw both teams’ assistant managers sent to the stands.
His exit followed an opening 18th-minute strike for Millwall from Aidan O’Brien, with Lee Gregory adding another before the break to leave Leeds with a mountain to climb.
But Christiansen’s team talk at the interval had the desired impact with a Pierre-Michel Lasogga double broken up by a 55th-minute Kemar Roofe equaliser to turn the game on its head and put the hosts in front just after the hour mark.
It was a lead they held until the closing minutes, only for the visitors to snatch all three points through strikes from Tom Elliott and Jed Wallace.
To add insult to injury for Christiansen on the disciplinary front, midfielder Kalvin Phillips collected a 10th yellow card of the season and will now serve a two-match suspension.
“I am very disappointed. Once again we go from this game without any points,” said Christiansen, who will take his squad to Spain next week for a training camp.
“Many ups and downs from the game, many emotions, but we cannot afford to lose our possibilities to do something good with red cards. They must stop now.
“We need to continue. You saw the response of the team in the second half. But unfortunately we shot ourselves in the foot and were one player less.
“The tactic for the next game is to start with one player less because that is when we play best!”