Millwall's unbeaten start to the new season came to a shuddering halt as Peterborough United produced a ruthless display in front of goal to condemn The Lions to their first defeat of the campaign.
Last season Posh recorded a 5-3 victory in the corresponding fixture at the ABAX Stadium, and the home side were once again on the front foot from the start of Tuesday night's match.
Millwall manager Neil Harris was unable to call on the services of midfielder Shaun Williams who sustained blurred vision in Saturday's draw at MK Dons - and it was The Lions who were seeing double as Posh stormed into a two-goal lead with a brace of goals in just 60 first-half seconds.
The home side had already shown their attacking intent with a bright start in which Paul Taylor dragged an effort wide of the target, but it took just six minutes for Posh to open their account when Marcus Maddison's left-foot cross-shot caught keeper Jordan Archer wrong-footed and the ball flew past a crowd of players into the back of the net.
With the home fans still celebrating, Millwall were caught out for a second time barely one minute later when the lively Taylor latched onto a neat Jermaine Anderson pass, and with the visiting defence caught square, he kept his cool to calmly slot the ball beyond the keeper's reach.
Millwall were reeling from this early blow and tried to hit back immediately with Steve Morison's shot curling off target and then midfielder Jimmy Abdou, in for the injured Williams, scooping an effort over the bar from a central position.
It didn't take long, however, for purposeful Posh to add a third goal and leave The Lions with a mountain to climb. Michael Smith whipped over an inviting delivery from the left and up popped the unmarked Gwion Edwards to steer a perfectly placed header into the roof of the net for the first of his two goals.
A hopeful volley from Ben Thompson and another shot from Morison that flashed high and wide of the target offered some hope to the travelling Lions fans who did their best to get behind the team in the opening half, but it was to no avail as Posh comfortably saw out the first 45 minutes to take a 3-0 advantage in at the break.
Harris introduced Gregg Wylde for Joe Martin at the break in a move that saw Shane Ferguson drop to left-back and the sub take his place on the left flank, and The Lions started in positive fashion with Lee Gregory forcing a smart save from Posh keeper Ben Alnwick, who pushed the striker's powerful effort over the bar for a corner.
However any hopes of a second-half fightback were quickly quashed and by the 52nd-minute, The Lions found themselves trailing 4-0. It was a goal of sheer simplicity too - a low cross from the right from Tom Nichols and Edwards nipped in between Webster and Tony Craig to gleefully slot into the gaping net.
Matters went from bad to worse for the visitors and it was 5-0 on 67 minutes, although Posh's fifth goal was slightly fortuitous; Anderson's initial shot was parried by Archer, but the ball fell kindly for Nichols, who could hardly miss as he stabbed the ball home from six yards.
Although Morison did pull a goal back for The Lions with 11 minutes remaining - a low right-foot finish into the opposite corner - it was too little too late on an instantly forgettable night for Millwall.
Peterborough United: Alnwick, Smith, Hughes, Bostwick, Baldwin, Edwards (Nabi, 75mins), Forrester, Taylor (Coulthirst, 74mins), Maddison, Anderson, Nichols (Gormley, 86mins). Subs not used: Santos, Tyler, White, Chettle.
Bookings: Baldwin (45+1min), Anderson (54mins)
Scorers: Maddison (6mins), Taylor (7mins), Edwards (20, 52mins), Nichols (67mins)
Archer, Martin (Wylde, 46mins), Craig, Thompson, Gregory, Romeo, Webster, Ferguson (Hutchinson, 77mins), Morison, O'Brien (Onyedinma, 65mins), Abdou. Subs not used: Worrall, Nelson, Philpot, King.
Martin (30mins), Abdou (58mins)
5,007 (away 648)