Millwall bowed out of the Capital One Cup at the first hurdle as League One side Crawley Town eased through 4-1 on penalties to book their place in the second round draw.
In a topsy-turvy encounter the Reds took an early lead through Hope Akpan (16mins) with Darren Ward (23mins) levelling for The Lions.
Crawley edged 2-1 ahead with a sublime strike from Nicky Adams (56mins) only for Kenny Jackett's side to claw their way back for a second time courtesy of sub Shaun Batt's 84th-minute strike.
Both sides had opportunities to win it in extra-time, but neither could capitalise and it was left to a nail-biting penalty shoot-out to send the visitors to a famous victory.
With the Championship season starting in just four days, a gruelling 120 minutes and defeat was perhaps not the way manager Jackett had envisaged going into Saturday's League opener against Blackpool.
The Lions manager handed two of his four summer signings a home debut with Chris Taylor and Scott Malone in the starting XI.
But it was former Lion Gary Alexander who nearly marked his return to The Den with an early assist, setting up Billy Clarke with a smart lay-off inside the opening five minutes, but the latter dragged his effort wide of the mark from 16 yards.
Millwall enjoyed a spell of pressure and conjured up a couple of openings themselves.
Jack Smith's delivery on eight minutes hung invitingly in the air for Darius Henderson, but he took a tumble in the area and the ball was cleared for a corner.
From the resulting set-piece, James Henry's cross picked out Ward and his header was deflected for another corner which was comfortably dealt with by the visiting defence.
Henry saw a stinging free-kick parried by Paul Jones in the Crawley goal with skipper for the night Liam Trotter just unable to keep the loose ball in play as The Lions threatened again.
But it was Crawley who broke the deadlock just past the quarter hour mark courtesy of Akpan's flicked header direct from a corner.
That advantage lasted just eight minutes though as Ward's deft header from a delightful Liam Feeney delivery hauled The Lions level.
And that is how the score remained going into half-time with the two defences remaining on top.
After a quiet opening to the second period the game sprung to life in a 60 second spell around the 55th-minute.
Henderson met Henry's cross deep in the danger zone, but his lay-off for Taylor was just too strong with the goal gaping.
Within less than a minute Crawley had edged ahead for a second time with Adams cutting in from the right and despatching a fine curling effort that nestled into the top left corner with Lions keeper Maik Taylor stranded.
Jackett shuffled his playing pack, bringing on Shittu and Batt for Feeney and Taylor.
Shane Lowry moved from centre half to left-back to accomodate Shittu and Malone moved further up field to take care of left midfield.
However, the duo had barely broken sweat when it could have been 3-1 to the visitors as Alexander swept
home from 10 yards, but the goal was ruled out for the narrowest of off-side decisions.
That was the wake up call Millwall needed and the home side so nearly equalised 20 minutes from time when Batt's close range effort was parried and Malone's follow-up hacked off the line.
On 73 minutes Henderson powered a free header from Henry's corner narrowly over and the front man went even closer five minutes later, but dragged a left-foot effort wide from 12 yards following good work by right-back Jack Smith.
But there was to be no denying Millwall, and with just six minutes of normal time remaining sub Batt - who really impressed after he came on - gleefully slamming the ball into the roof of the net from close range.
Extra-time failed to seperate the two teams either, but they both created gilt-edged chances to clinch victory.
The linesman's flag denied Henderson, who was adjudged to have fouled Kyle McFadzean as he tumbled into the back of the net taking the ball with him before Alexander blasted a whisker over and Crawley sub John Akinde, under pressure from Shittu, blasted well over with the goal at his mercy.
However, Henderson squandered an equally glorious opportunity in the dying moments of extra-time, controlling Malone's diagonal pass, spinning past his marker but then contriving to fire wide from eight yards.
And so to the dreaded penalty shoot-out in which Crawley were clinical, confidently converting their first three spot kicks, with only Trotter managing to hit the back of the net for Millwall.
Up stepped David Hunt for the visitors, knowing that if he scored Crawley would be through - and he confidently sent Taylor the wrong way to secure victory.
Millwall:M. Taylor, Smith, Malone, Ward, Lowry, Feeney (Shittu, 60mins), Abdou, Trotter, Henderson, C. Taylor (Batt, 60mins), Henry (Wright, 108mins). Subs not used: Mildenhall, Dunne, Racon, Marquis.
Bookings: Abdou (58mins), Batt (105mins)
Scorers: Ward (23mins), Batt (84mins)
Crawley Town: Jones, Sadler, Connolly (Hunt, 73mins), McFadzean, Akpan, Alexander, Clarke (Torres, 83mins), Simpson, Bulman, Adams (Akinde, 99mins), Davis. Subs not used: Kuipers, Cooper, Akinde, Wassmer, Neilson.
Booking: Akinde (100mins)
Scorers: Akpan (16mins), Adams (56mins)
Ref: D. Whitestone
Att: 4,050 (away 453)