Sub Steven Davies stepped off the bench to grab a late winner and condemn Millwall to their first away defeat in eight games at promotion rivals Bradford City.
There were just 11 minutes remaining when Davies rose to head home the only goal of a scrappy game dominated by awful weather conditions.
It was tough on a Lions side who battled throughout, but were ruthlessly punished by a Bantams outfit who have now moved into the top six, just one place and one point behind fifth-placed Millwall.
With two big matches against promotion rivals in three days, Lions boss Neil Harris made four changes to the team that started against Sheffield United.
Two of those were enforced, with Shaun Williams and Ed Upson replacing Shane Ferguson and Jimmy Abdou, both of whom were away on international duty, whilst Aiden O'Brien and Fred Onyedinma came in for Chris Taylor and Lee Gregory.
Prior to kick-off there was a one-minute silence impeccably observed to remember the tragic events in Brussels earlier this week.
Once referee Darren Bond blew his whistle to start the game the noise in a bumper home crowd, boosted by around 500 Lions fans, cranked up a few notches.
The swirling wind and sticky pitch didn't make for ideal conditions, but both teams tried to get to grips with it as best they could.
It was Millwall who pressed in the opening stages and The Lions were appealing for a penalty after two minutes when Onyedinma appeared to have his heels clipped as he tried to turn on a loose ball just inside the 18-yard box.
Midfielder Williams then had an effort that took a deflection on its way into the hands of Bantams keeper Ben Williams.
Bradford were a whisker away from taking the lead on six minutes when Tony McMahon's 20-yard free-kick curled inches wide off Jordan Archer's left hand post.
Moments later Jamie Proctor's header from Stephen Darby's cross took a bounce before Archer collected.
Joe Martin was somewhat unlucky to receive a yellow card on 13 minutes when a routine shoulder-to-shoulder tussle with McMahon saw the Bradford man go to ground easily, and with the home crowd baying for a red card, referee Bond - who was unsighted - reached for his book.
Upson was the next Millwall man to be punished, this time for a clumsy challenge on the halfway line, before Mr Bond dished out the third booking of the game after 22 minutes for a chest high challenge by Darby on Williams.
Lions left-back Martin had been inches away from breaking the deadlock just seconds earlier with a sweetly struck free-kick 18 yards out.
Scoring chances were at a premium in an opening half high on effort and endeavour, but sometimes lacking in that little bit of quality in the final third.
However The Lions did enjoy a spell of pressure before the break and created the best opportunity that could have brought the opening goal. A lovely spin from Steve Morison on the right took him past his marker, he volleyed the ball across the face of goal and O'Brien snatched at his shot, scooping his shot over the bar from eight yards.
Neither manager made any changes at the break and it was Bradford who were denied the first goal of the game by the reactions of keeper Archer, who saved superbly at point-blank range to deny Proctor before the linesman's flag came to the rescue, flagging to rule out Proctor's second effort after Billy Clarke had squared the loose ball into his path.
The Lions replaced Upson with Taylor with the second-half 12 minutes old in a bid to try and plunder some success on the left flank.
Taylor's first few touches came a minute later when he squeezed a low ball into the danger area that was hoofed clear by the boot of a Bantams defender.
Harris introduced top scorer Gregory to the fray just past the hour mark and then Bradford made a double change with James Hanson and Davies replacing Proctor and Clarke as the two teams looked to push on in search of a winning goal.
It was Bradford who made the crucial breakthrough when Davies, with virtually his first touch, stole in to head home Nathan Clarke's 79th-minute cross after Meredith's quick throw-in had caught The Lions napping.
On came Jamie Philpot for Millwall with Harris' last roll of the dice in a desperate bid to salvage a point from the game, Morison was denied an equaliser with four minutes remaining when keeper Williams flung himself across goal to brilliantly tip the skipper's goal-bound shot away and then Gregory's teasing delivery across the face of goal was begging for a touch as The Lions turned the screw.
But hard as they tried, the visitors just could not find that bit of magic to prise open the home defence and must now quickly turn their attention to Monday's home game with table-topping Burton Albion.
Bradford City: Williams, Darby, N.Clarke, Burke, Meredith, McMahon, Thorpe, Knott, Reid (90+2mins), B.Clarke (Davies, 73mins), Proctor (Hanson, 73mins). Subs not used: Cracknell, Routis, Anderson, Thomas.