An incredible finish saw Sheffield United spill two promotion points and Millwall gain one in battle to stay up.
Neil Harris's side missed a penalty in the 85th minute but still snatched a point through Jake Cooper late in stoppage time.
It was no less than the Lions deserved as United clung on to Gary Madine's 51st minute breakthrough. But it was a major blow for the Blades.
Millwall players celebrated with their fans in the stands after Jake Cooper's last-gasp equaliser
Cooper bundled the ball in the net from close range to send the away fans in pandemonium
Sheffield United boss Chris Wilder had some choice words for the officials at the end
Ben Marshall missed a penalty during the second half with his effort crashing off the crossbar
Gary Madine's composed finish had given the home side the lead early on in the second half
Madine had made a timely atonement for a three match ban as United kept playing leapfrog in the battle for automatic promotion.
But the real drama was at the end as Millwall substitute Ben Marshall missed a penalty in a heart-stopping moment for the Bramall Lane crowd.
With John Egan having been sent off for handling on the line, United's ten men still faced a frenzied finale.
And when substitute Tom Elliott's header was parried by Dean Henderson Jake Cooper followed up to score.
Wilder was clearly unhappy with an element to it and had sharp words with referee David Webb on the field at the end.
Madine's comeback from the bench had threatened to haul Chris Wilder's side back above Leeds ahead of the teatime game at Elland Road.
After a flat first half, Madine rewarded United's rampaging start to the second.
That 51st minute goal saw United squeeze out a previous victory.
With rivals Leeds playing later, the Blades were back on the see-saw for second spot, aiming to tilt the race back in their favour.
They had suffered a rare defeat in their last home game, going down 3-2 to Bristol City.
Another slip-up would be much more unexpected considering Millwall's battle to avoid the drop.
The Lions started out just two points clear of the bottom three. But they arrived on the back of decent form - only one defeat in the previous five and that was in a 3-2 cliffhanger at Leeds.
Sheffield United (3-5-2): Henderson,
