Their eight-match unbeaten run at Hillsborough came to an end in the final fixture of the calendar year, with Cardiff City denting the Owls' promotion hopes.
Wednesday, without top-scorer Steven Fletcher (illness) for the third match on the bounce, paid the price for a sloppy start as the Bluebirds raced into a two-goal lead inside the opening eight minutes.
A quickly taken free kick caught the Owls for the Bluebirds opener.
Lee Tomlin clipped the ball into the box for lone striker Robert Glatzel, who shrugged off the attentions of Dominic Iorfa and Liam Palmer before drilling a low left foot shot past Cameron Dawson.
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Tomlin was the architect of Cardiff's second, fizzing in a dangerous cross from the right for Junior Hoilett to tap in at the far post.
Wednesday boss Garry Monk said: “They were poor goals to concede from our point of view.”
It took a superb block from Jazz Richards to stop recalled Wednesday striker Sam Winnall from pulling one back following a good raid down the right by Jacob Murphy. Barry Bannan's follow up effort was acrobatically tipped over the bar by Neil Etheridge.
But skipper Tom Lees reduced their arrears, rising highest at the back post to nod home Bannan's corner to claim his second goal in as many outings.
There was a long break in play after a clash of heads between Hoilett and Joe Bennett.
Ex-Owls loanee Bennett was eventually stretchered off as the Bluebirds were forced to rejig their defence.
Nathaniel Mendez-Laing was also withdrawn after sustaining a knock as Cardiff switched to a 5-4-1 formation.
Wednesday dominated possession and territory in the first half, but Cardiff's patched up team held firm.
Leandro Bacuna was in the right place at the right time to clear Lees' shot off the line as the Owls pressed for an equaliser.
And the Bluebirds almost snatched a third deep into added on time in the first half, Glatzel sliding in at the back post to steer narrowly wide from a long throw in.
There was a major flashpoint just after the hour mark following a rash challenge by Hoilett on Liam Palmer near the halfway line.
Hoilett cleaned the Owls full-back out but referee Tim Robinson only deemed it worthy of a yellow card.
Robinson's decision angered Wednesday's coaching staff and the home contingent, who felt it should have been a straight red.
Palmer was unable to continue and had to be helped down the tunnel by the Owls' medical team.
“It was a red card,” bemoaned Monk.
“It was reckless and out of control.
“I have got a player sat in the treatment room with an ankle the size of a balloon.
“I don’t understand how the ref came to that decision.”
Inspired by substitute Sol Bamba, Cardiff repelled everything the Owls had to throw at them in a scrappy second period.
Wednesday looked bereft of ideas in the final third and lacked the guile and imagination to unlock the visitors stubborn rearguard.
There was a late flurry from the Owls, with Adam Reach, Jacob Murphy and Atdhe Nuhiu spurning opportunities.
Monk said: “We pushed and tried in the second half but, with the set up they had, we couldn’t quite find that final ball.”
Wednesday head into 2020 on the back of consecutive defeats and clinging on to a play-off spot in a congested second-tier.