The January signing from Wolverhampton Wanderers marked his debut by poking in an equaliser in the tenth minute of stoppage time.
It meant heartbreak for the Millers, who had been the better team and created the better chances.
A familiar failure to capitalise when on top, however, came back to haunt Paul Warne’s men as the Owls preserved their remarkable record in Rotherham.
It is 43 years since Wednesday last lost away from home against the Millers. Those 12 visits have now yielded nine wins and three draws.
Two goals inside 87 seconds capped an entertaining first half. The Owls took the lead through Fernando Forestieri on 37 minutes but were pegged back almost instantly through Jon Taylor.
On the balance of play, Rotherham should really have had an iron-grip on proceedings before Forestieri made the breakthrough but poor finishing cost Paul Warne’s men.
Michael Smith’s miss was the worst of the trio that let Wednesday off the hook.
Teed up by Michael Ihiekwe and just 12 yards out, the Millers striker side-footed a shot wide of the target when he simply had to hit the target.
Moments earlier, Anthony Forde had been denied by Keiren Westwood when one-on-one with the goalkeeper after dispossessing Michael Hector.
Wednesday’s hat-trick of let-offs was completed just after the half-hour, Joe Mattock firing high and wide when well placed.
Adam Reach then hit the post as the Owls finally stirred in attack before Forestieri finished with aplomb.
The Millers raced up the other end and Taylor volleyed in from a Smith cross.
United had the better of the chances in the second half. First, a length of the field break by Will Vaulks ended with Towell spurning a great opening, the Millers man allowing himself to be crowded out.
Then, Reach had to clear from under his own crossbar after Semi Ajayi had thundered a header goalwards from a corner.
In this instance, however, Wednesday’s reprieve was only temporary as another sweeping move led to the home side’s second goal.
Joe Newell latched on to a header from Michael Hector before rolling a pass that Smith was unable to control. Quick as a flash, though, Towell swooped to fire in off the inside of the post.
Smith should have wrapped up matters nine minutes from time but he headed wide when well placed.
His profligacy came back to haunt Wednesday when Iorfa prodded in following a scramble to spark wild celebratory scenes among the 2,625 away fans that ended with Forestieri being shown a second yellow card of the afternoon and being dismissed.