NEWCASTLE 0 SHEFF WED 1
26. Karl Darlow
8. Vurnon Anita
6. Jamaal Lascelles
2. Ciaran Clark
3. Paul Dummett
11. Matt Ritchie
14. Isaac Hayden
4. Jack Colback 80'
20. Yoan Gouffran 62'
15. Mohamed Diame 69'
9. Dwight Gayle
Subs
7. Achraf Lazaar
17. Ayoze Perez 69'
18. Chancel Mbemba
22. DeAndre Yedlin
28. Matz Sels
30. Christian Atsu 62'
45. Aleksandar Mitrovic 80'
Leaders Newcastle missed the chance to go four points clear at the top of the Sky Bet Championship on Boxing Day.
The Magpies slipped to their first league defeat to Sheffield Wednesday since 1998 as they went down 1-0 at St James' Park.
Owls captain Glenn Loovens' second-half header separated the two sides as play-off chasing Wednesday picked up the points.
Newcastle boss Rafa Benitez named three changes to the team that won at Burton last time out.
Jonjo Shelvey started his five-match ban after deciding against contesting his racial abuse charge, while DeAndre Yedlin and Christian Atsu also missed out.
Vurnon Anita, Jack Colback and Yoan Gouffran were the trio who came in for the clash.
Wednesday's Carlos Carvalhal also made three changes with Almen Abdi, Kieran Lee and Lucas Joao dropping out for Ross Wallace, Barry Bannan and Fernando Forestieri coming into the side.
Newcastle piled on the pressure early on as they created the bulk of the chances.
Magpies goalkeeper Karl Darlow had to be at his best as he pulled off numerous saves before the break.
Both sides were tentative early on before Dwight Gayle, the league's top goalscorer, saw Owls stopper Keiren Westwood tip his strike onto the crossbar.
Newcastle defender Ciaran Clark headed off target twice from corners, with the first flying over the bar before the second went wide of the target.
Scottish striker Steven Fletcher, who plied his trade at Newcastle's arch-rivals Sunderland for four seasons, forced Darlow into a top stop to tip his thunderous shot over.
Just before the break Benitez's men had two shouts for penalties waved away by referee Paul Tierney.
The first came after lots of shirt pulling following a free-kick, before Matt Ritchie went down in the box minutes later.
Moments after the restart Darlow had to make another stellar save to keep out Fletcher with his legs.
In the 53rd minute Wednesday grabbed the only goal of the game through Dutch defender Loovens, who netted his first Owls goal, as he nodded home the rebound from Forestieri's initial header.
Wednesday looked content with a one-goal win as they kept men behind the ball after scoring and invited the hosts' onslaught.
The Magpies looked to force an equaliser and on the hour mark they came close with Isaac Hayden hitting over the bar before Gouffran glanced a header wide.
With 15 minutes left on the clock Westwood pulled off a stunning stop to tip Atsu's rasping effort over and Wednesday held on for three crucial points in their promotion bid.