DJ Campbell marked his Millwall debut with a late leveller as Tuesday night's basement battle ended all-square - and with both teams down to 10 men.
Wednesday sub Giles Coke put the Owls ahead midway through the second-half but the visitors were pegged back by a diving header from fellow sub Campbell 10 minutes from time.
A feisty encounter then boiled over with barely two minutes remaining when Coke went from Owls hero to zero when he was red-carded following a clash off the ball with Shane Lowry, who was also sent packing by the referee.
Millwall were left with a real sense of frustration at the final whistle, having not only created the best chances of the game, but also seeing two contentious penalty decisions go against them.
Lions boss Ian Holloway made two changes to the side that beat at Ipswich with keeper David Forde (injured) and striker Scott McDonald (rested) replaced by Stephen Bywater and Martyn Woolford.
Millwall impressed in the opening exchanges with keeper Chris Kirkland saving Dan Shittu's header from a Lee Martin corner before Steve Morison lashed the ball across the face of goal.
It took a smart save from Kirkland to thwart Martin, who capitalised on a lapse of concentration in the visiting defence to break clear through with just the keeper to beat.
However Holloway's men had a lucky let-off on 28 minutes when Atdhe Nuhiu headed Jeremy Helan’s teasing cross narrowly over from six yards.
Chris Maguire tried his luck from distance, but fired narrowly over moments after Martin had again seen a close range effort smartly saved by Kirkland.
The Wednesday keeper produced a stunning save shortly after the break, arcing backwards to somehow scoop Morison's looping header over for a corner.
Lions stopper Bywater was nearly left red-faced when he let Caolan Lavery's cross squirm out of his hands and so nearly over the goal-line, but the danger was thankfully averted.
However there was little the keeper could do to prevent Wednesday taking the lead on 69 minutes when Coke latched onto Maguire's threaded throughball, rounded Bywater and rolled the ball into the back of the net.
Bywater kept The Lions right in contention moments later when he superbly tipped Miguel Llera's goalbound header over the bar.
The Lions were left rueing their luck on 76 minutes again. Having already seen a 64th-minute penalty appeal turned down when debutant Shaun Williams tried to connect with Martyn Woolford's cross, fellow new-boy Campbell was also sent to ground as he prepared to shoot eight yards out.
Millwall's never-say-die spirit was eventually rewarded 10 minutes from time when Campbell headed home the rebound from close range after Liam Trotter's header had canoned off the woodwork.
With three priceless points up for grabs tensions - and tempers - rose heading towards the final whistle with Coke and Lowry dismissed for squaring up to each other sparking an incident that resulted in yellow cards for Bywater and Nuhiu too.
The eight minutes of injury-time could have seen another sending off when keeper Kirkland clearly handled the ball after racing out of his area, but the officials appeared unsighted.
Morison's low grubber was then saved by Kirkland, but hard as The Lions tried to find a way through for a second time, it was not to be and the spoils were shared.
Bywater, Fredericks, Malone, Bailey (Williams, 60mins), Shittu, Lowry, Martin (Feeney, 65mins), Trotter, Morison, Woolford, Keogh (Campbell, 6mins). Subs not used: Gerrar, Dunne, Beevers, Marquis.
Bookings: Martin (43mins), Bywater (88mins)
Sending off: Lowry (88mins)
Sheffield Wednesday: Kirkland, Palmer, Loovens (Lavery, 46mins), Onyewu, Helan, McPhail (Coke, 59mins), Lee, Maguire, Llera, Nuhiu, Semedo. Subs not used: Martinez, Corry, McCabe, Maghoma, Stobbs.
Ref: L. Probert
Att: 10,624 (away 1,049)