Fleetwood Town fired a derby day warning shot as they ended Millwall's nine-game unbeaten run.
Town's inconsistency has been all too apparent this campaign.
And, after Saturday's demolition job against Swindon, the Lions looked a tough prospect.
Neil Harris' men arrived at Highbury as League One's away day specialists.
Not that Steven Pressley's men seemed troubled by such a fact - upping their pressing game, their tempo, their desire to claim a vital win.
The Lions, as expected were an altogether different animal to Saturday's opponents, more aggressive around the ball working hard to deny Fleetwood the chance to play around their box.
Even so, Town made a bright start, carrying the confidence of Saturday's convincing victory into the game.
Tariqe Fosu's enthusiasm made life difficult for full back Shaun Cummings, the on-loan Reading winger keen to keep building his partnership with David Ball.
Fosu's tricky feet earned Fleetwood an early free kick, from which they should have made more.
But the hosts continued to apply the pressure and should have taken an early lead.
Ball flicked a neat pass into the path of David Henen, the Everton forward's run taking him behind Millwall lines.
But the striker's touch was too heavy, inviting Jordan Archer into the challenge, the Lions keeper sliding to meet his foe just as the trigger was being pulled.
Fleetwood weren't having it entirely their own way - a string of hopeful percentage balls carrying too much to make use of even Fosu's pace.
But Steven Pressley's men looked a threat, Nathan Pond forcing a vital clearance with a flicked near-post header as Fosu rifled in a corner from the left.
Millwall got lucky in the pinball which followed, clearing their lines and halting a Henen charge from the opposite flank.
Town were certainly enjoying the better of the possession and the chances but the visitors gradually cranked up the pressure, advancing their line and trying to force Fleetwood into errors in their final third.
In a swirling wind and driving rain it very nearly paid off, a deflected ball bouncing into the box, momentarily wrong-footing Chris Maxwell.
He wasn't the only man confused by the flight, Millwall unable to make a real chance, a hopeful ball knocked backwards the best they managed, Town eventually mopping up but earning a stern ticking off from their manager.
The aerial approach was out but fortunately Fleetwood have some clever feet and quick minds - Henen setting up another clear-cut chance with a beauty of a backheel.
Sarcevic was the man who gave chase, making the ground but unable to apply any real power to his shot, Archer stopping but spilling the wet ball, David Ball adjudged to have fouled the Lions keeper as he tried to take advantage.
Fleetwood were undoubtedly dominant but unable to find they way past a stubborn back line.
And the Lions's stubborn will nearly paid off moments before the break.
The visitors looked potent on the break, direct balls from the back causing issues for Town.
But none could have predicted what would happen with Steve Morison got a head on a punt forward 30 yards from goal.
His effort looped over Maxwell, dropping, dropping, almost looking like creeping in, the bar coming to Town's rescue, the scores level at the interval.
It might have been the confidence boost Millwall needed, the Lions starting the second half with a little more belief.
And Aiden O'Brian, anonymous before the interval could have handed them the advantage, slipping between defenders and applying a boot to a long throw, the effort flying over the crossbar.
It was a warning shot to Fleetwood who continued to make their pressing game work, winning a string of corners as Millwall dug in - block after block keeping Fleetwood at bay as Henen and Fosu buzzed excitedly around the fringes.
And eventually pressure was made to count.
Eggert Jonsson's performances have been improving week on week, his confidence as a League One player growing.
The Icelander had already fired a warning shot, Archer forced to tip his 18 yard effort over the bar as Millwall buckled.
From the resulting corner Town kept the ball around the visitors' box, Fosu eventually finding space to cross from the right, Jonsson arriving at full stretch, diving in at the back post and apply a bullet header.
Town had the advantage and weren't going to let go without a fight.
Millwall were rattled, giving up a sloppy opportunity when Archer cleared straight into the path of Fosu.
Joe Martin took one for the team, felling the Fleetwood flyer.
But even then the on-loan wide man wasn't done, trying his luck direct from the set piece, Archer very nearly caught out, moving late to collect the cheeky attempt.
Town did eventually make it two - Bobby Grant combining the sublime and the bizarre to put the game beyond doubt.
His corner might well have been caught by a gust, Archer completely wrong-footed as the ball seemed to drift straight in at the near post - no sign of contact from any other party, Grant only too happy to claim, the plaudits.
That should have been that - Fleetwood in the clear with minutes remaining.
But Town are not yet the finished article and the Lions left a sour taste and ensured a tense ending with a goal in the fourth of five added minutes.
With Conor McLaughlin taken off, once again suffering concussion, Fleetwood were light down the right, conceding a corner.
The drilled cross was Millwall's best delivery of the night, Byron Webster pouncing at the back post and powering home.
It was a mere consolation but one which will upset Fleetwood's defence who have twice in four days been denied a clean sheet by a lax moment late on.
Fleetwood now move on to a derby day - taking masses of confidence into their trip to Bloomfield Road.
Beyond that they climb away from the drop zone, confidence and belief building,.
The arrival of Henen and Fosu has undoubtedly given Town more bite up front.
But the transformation in the past fortnight goes deeper - Fleetwood inspired all over the field, knowing they have an outlet or two making all the different.
Fleetwood are far from out of the woods but should they repeat their last two displays at Bloomfield Road on Saturday, Blackpool should be very worried indeed.