Marten de Roon fired Middlesbrough to victory in the desperation derby as Sunderland's hopes of another remarkable Premier League escape were dealt a potentially fatal blow.
The 26-year-old Dutchman, a £12million summer signing from Atalanta, struck just nine minutes into a tense relegation showdown between the bottom two to secure a first league win since December 17 and leave the locals among a crowd of 30,742 daring to believe survival is a possibility for their club.
It remains a tall order, with Steve Agnew's men still six points adrift of safety with only four matches to go, but they are significantly better off than the Black Cats, who are six points further adrift with just a single game in hand.
Sunderland started with purpose, forcing two early corners and then prompting the game's first save when Brad Guzan had to react smartly to field Jermain Defoe's well-struck seventh-minute volley.
However, their hopes were dealt a significant blow when Boro forced their way ahead two minutes later without having to work particularly hard for it.
Adam Clayton's ball over the top left defenders Billy Jones and John O'Shea trailing in De Roon's wake and he controlled with his chest before stabbing a shot past the advancing Jordan Pickford.
The Teessiders visibly grew in confidence as the Black Cats deflated and they might have doubled their lead with 20 minutes gone when Stewart Downing pounced on an error by Jones to race in on goal, where Pickford made a vital block.
Sunderland were in disarray as Clayton conducted proceedings from just in front of his back four with De Roon and Adam Forshaw foraging ahead of him, and full-back Calum Chambers whistled a 23rd-minute effort from distance just high and wide.
To their credit, the visitors eased themselves back into the game and although chances were at a premium - Didier Ndong called upon Guzan with a rasping effort 11 minutes before the break - they at least did enough to suggest they had not thrown in the towel.
Guzan had to palm away Wahbi Khazri's 48th-minute free-kick after Daniel Ayala's clumsy challenge on Victor Anichebe 20 yards out, and skipper Ben Gibson had to be alert to prevent Anichebe from connecting with the Tunisia international's cross four minutes later.
Sunderland continued to enjoy the better of the second half, with Defoe seeing a shot on the turn blocked from Anichebe's 59th-minute cross as a nervy Boro retreated, although they gradually managed to stem the tide as Agnew anxiously paced about in his technical area.
Opposite number David Moyes, who had earlier been handed a Football Association charge over comments made to a female reporter last month, stood hands in pockets yards away seemingly powerless to halt the slide towards the Sky Bet Championship.
He waited in vain for a late fightback as Boro eased themselves over the line with few scares to fight another day.