Manchester City's hopes of retaining the Premier League title are in tatters after their former midfielder Adam Johnson fired Sunderland to a shock 1-0 win over the champions on Wednesday.
Roberto Mancini's side wasted a chance to keep the pressure on Manchester United at the top and they are now seven points behind the leaders, who scored a late winner to beat Newcastle 4-3.
Johnson's 53rd-minute winner eased Sunderland's relegation fears as the England international profited from a rare error by goalkeeper Joe Hart to hand City their first away league defeat since April.
With City protesting at a foul on Pablo Zabaleta in the build-up, Johnson accepted a pass from defender Carlos Cuellar to cut in from the right past David Silva and fire in a low shot which should have been collected by Hart.
However, he was guilty of failing to cover his near post, allowing the ball to creep into the bottom corner under his outstretched left hand.
Stephane Sessegnon should have doubled the lead within moments, dragging a clear chance across the face of goal, before Hart partly made amends, blocking with his feet as the Benin international raced onto a through-ball from Fraizer Campbell to see his first-time shot denied.
Sunderland's margin of victory could have been more clear cut, with substitute Campbell spurning a close-range chance to double the lead seven minutes from time.
It's now almost four-and-a-half years since City have won at the Stadium of Light, with the pain of defeat heightened after the loss was inflicted by one of their old boys.
Despite earning a title-winner's medal with City, Johnson enjoyed mixed fortunes in a two-and-a-half-year spell at Eastlands, returning to his native North-East in a £10 million move in August after making just 39 top flight starts.
The 25-year-old has struggled to scale the heights in the first half of the season, but helped his bid to win over the Wearside faithful with a goal that could have ramifications at both ends of the season at the end of the campaign.
City skipper Vincent Kompany came up from the back to send an early header from 10 yards against the bar from Silva's corner, with keeper Simon Mignolet using his feet to save the close-range follow-up from Yaya Toure.
Mignolet was called into action again, this time with an agile save to pluck a 25-yard effort from Yaya Toure out of the air that was destined for the top corner.
Mignolet rounded off an impressive first-half with a fine point-blank block to deny Silva, who arrived at the near post to deflect a Sergio Aguero cross towards goal in a swift counter-attack launched by an incisive 40-yard pass from Carlos Tevez.
It proved to be a much quieter half for Mignolet's opposite number Hart, but the City keeper was equal to the task in the only major threat to his goal before the break.
Steven Fletcher, the eight-goal top scorer, reacted first to a Sessegnon flick to fire in a firm 20-yard effort, but the low shot was brilliantly saved by England number one Hart diving to his right
Mignolet made a fine reaction save to deny Aguero after the Argentine beat Sunderland's offside trap to meet Silva's slide-rule pass.
But it was the hosts who looked more likely to add to Johnson's strike as the contest wore on in what proved to be a famous victory for Martin O'Neill's side.