Steve Morison thumped home a stunning goal from distance as Millwall kicked off 2018 at Norwich City.
The striker claimed his second goal in as many games just before the half-time break by firing home from 30-35 yards out, but that was to be in vain as second half strikes from Tom Trybull and James Maddison gave The Canaries all three points.
The second half performance left Neil Harris raging at full-time.
"To weather the storm after the first 20 minutes and to deny a really good footballing team to so few opportunities and then get our noses in front - the job is half done," he told millwallfc.co.uk.
"To then concede two goals in the manner we did - the second-half performance was a disgrace from my players. We didn't get near enough to the ball and the concession of the first goal is abysmal by us. To give away a free header in that position is not acceptable.
"I've left my players in no uncertain terms regarding my thoughts on that second-half. We need to be better than that."
The Lions certainly were in their next outing as they dumped fellow Championship side Barnsley out of the Emirates FA Cup at the Third Round stage with a 4-1 win.
Aiden O'Brien (2), Ben Thompson and Fred Onyedinma were on target as Harris made six changes to his starting line-up with David Martin, Conor McLaughlin, Tony Craig, Thompson, Jed Wallace and O'Brien replacing Jordan Archer, Mahlon Romeo, James Meredith, Ryan Tunnicliffe, George Saville and Lee Gregory.
Millwall extended their run to seven matches at The Den - beginning their 17-match run in the League without defeat in the process - with a 1-1 draw against Preston North End on 13th January.
O'Brien's fifth goal of the season looked to have given The Lions all three points, but Callum Robinson equalised 10 minutes from time to level proceedings.
Despite conceding late on, Harris was pleased with the point, commenting: "When you're 1-0 up at half-time at home, it's disappointing not to get all three points, naturally. But, against a competitive side, an aggressive side in the way they press, a team that are going to be in and around the top six at the end of the season, it's a good point."
What was to follow at Leeds United one week later would change the season and become an afternoon etched in the memory of Lions fans around the world.
A bumper crowd at Elland Road saw Millwall dominate their opponents and race into a 2-0 half-time lead courtesy of goals from O'Brien and Gregory, with Liam Cooper given his marching orders for the hosts.
However, when it looked as though The Lions would coast to victory, a remarkable turnaround saw The Whites swing the pendulum their way, scoring three goals in 16 second half minutes.
But, Millwall were not to be denied as firstly Tom Elliott and then Wallace - in the second minute of stoppage time - found the net to win the game 4-3 and secure a first away victory of the campaign.
The manager attempted to sum up a breathtaking encounter by saying: "I have contrasting emotions, I have to be honest. I thought my team in the first half - at 11v10 and 11v11 - were outstanding. Jordan Archer made a fine save early on to make sure we were in the game and then we could've gone on to score six or seven.
"At half-time and 2-0 up, I said to the boys to not step off - if they had come in at 6-0, it wouldn't have been a disgrace. At a place like Elland Road, it's all about character. Any momentum that Leeds get, they're going to feed off it.
"Fair play to Leeds, that was some hell of a performance by them to get on top. But there's no way we should be in that position. I'm delighted with the final outcome, but there's certainly a lot of learning for us to take from that."
It was back down to earth on the 27th as League One strugglers Rochdale visited The Den in the Fourth Round of the Emirates FA Cup.
Jed Wallace struck an early penalty-kick home to nudge The Lions towards Round Five, but Keith Hill's men had other ideas as goals from Ian Henderson and Matt Done put the away side in front as the hour-mark approached.
Thompson, however, shot home in the 90th minute to secure a replay and the prospect of a Den tie with either Tottenham Hotspur or Newport County in the next round.
A goalless draw with Derby County was to end the on-field action in January, but the biggest talking point was on the transfer front, as, in addition to Jason Shackell, Harry Toffolo and Ben Marshall, Tim Cahill returned home for the remainder of the campaign.