Mark Beevers and sub Lee Gregory struck second-half goals as Millwall maintained their unbeaten away record in League One with a superb win at Vale Park.
Defender Beevers headed The Lions into a 57th-minute lead with his first goal of the season and Gregory made the points safe in injury-time with a perfectly placed penalty after he had been fouled by keeper Jak Alnwick.
Ironically it had only been the brilliance of Vale keeper Alnwick that had kept the rampant Lions at bay in a game dominated by Neil Harris' men.
Showing just one change to the side that beat Crewe on Saturday - Byron Webster coming in for the injured Sid Nelson - Millwall really produced a performance brimming with pride, passion and attacking purpose.
Aiden O'Brien, a hat-trick hero at Crewe, so nearly picked up where he left off on in the opening two minutes. Strike partner Steve Morison did supremely well to cushion a header from Shaun Williams' pass into O'Brien's path and having had one stab at the ball, the striker's second attempt was arrowing for the top corner until a superb headed goal-line clearance from Ben Purkiss denied Millwall an early lead.
Such was The Lions' dominance that it is no exaggeration to say the visitors could have been 5-0 ahead in the opening quarter of an hour as they battered at the Vale defensive door, but could not find a way past keeper Alnwick, who was in inspired form, in the home goal.
O'Brien went close with a low drive after controlling Williams' pass but Alnwick was equal to his effort. The keeper came to the rescue again on 12 minutes when Fred Onyedinma touched the ball into Ed Upson's path and the midfielder's drive was somehow pushed away at full stretch.
Alnwick then produced a further two top class saves in the 14th and 15th minutes, first getting down low to gather Morison's header from Williams' corner before Morison and O'Brien set up Upson, who was thwarted by the agility of Alnwick once again.
Carlos Edwards led the charge on 28 minutes with a surging run down the right flank and his inviting delivery picked out Morison, whose powerful header was smartly gathered by Alnwick.
Morison was involved again two minutes later, beating the offside trap with a perfectly timed run and laid the ball into O'Brien's path who in turn fed Onyedinma. On this occasion the young winger's effort was deflected away for another corner.
Having played with such confidence and conviction, The Lions so nearly found themselves going a goal behind with Vale's only real scoring opportunity of the opening 45 minutes. Lions keeper Jordan Archer had pretty much a spectator for the first 45-minutes as the majority of play took place in midfield and, on a positive note, in the final third at the other end of the field.
It would have been a travesty had they gone in trailing at the break, but keeper Archer ensured that the score remained 0-0 with an acrobatic fingertip save to push Enoch Andoh's bullet close-range header over the bar.
Vale made one change at half-time, introducing Ryan Inniss for Remie Streete, but the game shaped up in near identical fashion to the first half with The Lions producing some quite outstanding attacking football.
Such was the confidence in the side that Jimmy Abdou tried his luck from 25-yards, as did Williams, whose rasping drive saw Alnwick fling himself across goal and turn the ball behind for a corner.
The home side struggled to get any attacking momentum going, but on a rare forward foray in the 56th-minute, Beevers broke up a promising attack with a splendidly timed tackle on the edge of the penalty area to win the ball off the toes of Byron Moore.
Less than 60 seconds later Beevers showed his worth at the other end, powering a textbook header from Williams' deep corner into the roof of the net, sparking wild celebrations between the players and 210 Lions fans situated behind the goal.
Having seen four Millwall players go into referee Oliver Langford's book, the worst tackle of the night - a raking challenge by Anthony Grant on Upson - was punished by a yellow card when on another occasion it may well have been red.
Not surprisingly as the game wore on Vale threw caution to the wind and piled forward in search of an equaliser.
The Lions stood firm, however, with the team working their socks off for each other and defending in numbers with Webster, Abdou and Beevers throwing their bodies on the line with brave blocks.
That work ethic was epitomised in the second minute of injury-time when sub Gregory quite simply refused to give up the ghost, losing possession and then winning it again in the penalty area before drawing a foul out of Alnwick.
Gregory picked himself up, dusted himself down and calmly slotted home the resulting spot-kick to put the seal on a top notch team performance from the rejuvenated Lions.
Port Vale: Alnwick, Purkiss, Dickinson, Duffy, Ikpeazu, Dodds (Leitch Smith 62mins), Foley (McCourt, 82mins), Moore, Streete (Inniss, 46mins), Andoh, grant. Subs not used: Johnson, Birchall, Daniel, Lloyd.
Archer, Edwards, Craig, Beevers, Webster, Abdou, Williams, Upson, Morison (Gregory, 67mins), O'Brien (Marquis, 82mins), Onyedinma (Ferguson, 76mins). Subs not used: Forde, Martin, Cowan-Hall, Thompson.
Williams (15mins), O'Brien (65mins), Webster (66mins),
Beevers (57mins), Gregory (90+2mins)
4,477 (away 210)