Wednesday upset the bookies and Barnsley with a vital 2-1 victory at Oakwell.
A Jordan Rhodes double did the damage to halt the hosts’ outstanding run of nine wins from 10 and give Darren Moore his first triumph to boot.
Substitute Carlton Morris halved the deficit but it was too little too late and the derby duel was won by Wednesday.
And it was no more than they deserved, turning in a measured and disciplined performance to breathe life into the battle against the drop.
The Owls had to overcome a blow when Keiren Westwood withdrew during the warm-up and it was almost a double whammy inside five minutes as Michael Sollbaeur spooned a clear chance over from close range.
Bur that proved Barnsley’s best chance of a first half that slowly and surely shifted the way of Wednesday.
And the Owls might have taken the lead on 20 minutes when Rhodes almost capitalised after Brad Collins came racing out of his goal but the shot from range was wide of the target.
But Wednesday pressed on, looking assured in and out of possession, and hit the front on 38 minutes.
Barry Bannan found space down the left and delivered a pinpoint cross onto the head of Rhodes, who glanced accurately beyond Collins.
The Owls protected their lead to the interval and the challenge was extending that resistance through the second half.
Barnsley made a triple change in a bid to revitalise their impetus and standing as the form team of the division – but to no avail as Wednesday made it 2-0 on 53 minutes.
Josh Windass and Rhodes broke free of the Barnsley backline and the former played in the latter with aplomb to double the advantage.
The hosts were forced further and further forward but Wednesday soaked up the pressure and if anything seemed the more likely on the counter.
But with 12 minutes to go it was the Reds that registered. A loose ball found its way to Morris, who unleased a fierce volley that flew past Wildsmith with the aid of a slight deflection.
That triggered an inevitable late push for the equaliser and Alex Mowatt went close with a curling set piece but the Owls stood their ground to show the relegation fight is far from over.
Wednesday: Wildsmith, Palmer, Lees, Urhoghide, Börner, Paterson, Reach, Bannan, Pelupessy, Windass (Green 84), Rhodes