Jake Cooper's injury-time leveller rescued a dramatic point for Millwall at Bramall Lane on Saturday afternoon as The Lions drew 1-1 with Sheffield United in the Sky Bet Championship.
Gary Madine opened the scoring six minutes into the second-half, but The Lions seemingly spurned a golden opportunity to claim a point late on as Ben Marshall crashed a penalty against the crossbar after John Egan saw red for deliberate handball.
Cooper, however, turned home a rebound deep into stoppage-time to secure a vital share of the spoils.
Neil Harris opted for two changes against The Blades, with James Meredith and Marshall making way for Conor McLaughlin, making his first start since 24th November, and Shane Ferguson, returning from suspension.
The home side enjoyed a spell of possession in the opening stages, but it was Millwall who had the first chance of note as Alex Pearce steered the ball wide from Ferguson's corner-kick.
A nervy atmosphere inside Bramall Lane could be sensed, and with 19 minutes on the clock The Lions could have been in front once more, but Cooper's header was blocked. At the other end, Enda Stevens failed to make a proper connection from a cross and glanced wide.
An injury to Chris Basham meant United had to change personnel and formation with just 21 minutes on the clock, with the next attempt coming shortly before the half-hour mark as David McGoldrick curled just wide of David Martin's post.
In what was a midfield battle for most of the half, United broke forward on 42 minutes and nearly found a way to goal through Stevens, but Cooper's tackle prevented Martin from being troubled. From the corner that followed, an effort bounced off Lee Gregory and towards goal, but the stopper was well placed to claim.
The Lions had to stand tall to some relentless pressure from the home side in the opening stages of the second-half, with a combination of the entire defence and Martin stopping United efforts from troubling the goal, but on 51 minutes The Blades gained the lead as John Fleck squared to Madine, who had an easy task of sliding into the net.
Millwall responded well, however, and made a chance of their own five minutes later, but Ryan Tunnicliffe was just beaten to the ball inside the six-yard box from Ben Thompson's cross.
Ex-Blade Ryan Leonard's shot was then deflected into the arms of Dean Henderson as Bramall Lane once again became nervy as the last 20 minutes loomed, with a further spell of Lions pressure ending courtesy of Jed Wallace's volley, which went wide.
McGoldrick then tested Martin at the other end, before Mahlon Romeo's piledriver forced Henderson to tip wide on 78 minutes. Substitute Tom Elliott then headed into the arms of the stopper as The Lions tried to force an equaliser - and their best chance came in the 85th minute as they were awarded a penalty-kick after Egan's deliberate handball on the line.
Marshall stepped up to take, but smacked his effort against the crossbar and over.
Millwall were still attacking deep into injury-time and Henderson had to save from Cooper, but the defender was to have the last laugh as he turned Marshall's cross home after Elliott's initial header was saved by the goalkeeper four minutes into stoppage-time.
Sheffield United: Henderson, Stevens, Fleck, O'Connell, Basham (Madine 21'), Sharp (Craine 64'), Egan, Norwood, McGoldrick, Freeman, Duffy (Coutts 72'). Subs not used: Dowell, Hogan, Madine, Stearman, Moore.
Scorer: Madine 51'
Sent Off: Egan
Millwall: Martin, McLaughlin (Marshall 58'), Cooper, J. Wallace, Thompson, Gregory, Ferguson, Romeo (O'Brien 81'), Pearce, Tunnicliffe (Elliott 69'), Leonard. Subs not used: Amos, Meredith, Williams, Morison.
Scorer: Cooper 90+4'
Booking: J. Wallace
Referee: David Webb
Attendance: 26,703 (661)