South Korea's Ji Dong-Won struck in injury time as Sunderland inflicted a shock 1-0 defeat upon Premier League leaders Manchester City at the Stadium of Light here on Sunday.
The result left Roberto Mancini's expensively assembled side ahead of second-placed Manchester United on goal difference alone after the champions' equally surprising 3-2 loss at home to strugglers Blackburn on Saturday.
Not even the introduction of Sergio Aguero and David Silva in the second half could inspire City to the victory their Italian manager craved.
And it was Ji, a Sunderland substitute, who was the surprise match-winner when he finished off a terrific counter attack in the third minute of stoppage-time to snatch victory for the Black Cats, who are now six points above the relegation zone.
With enigmatic forward Mario Balotelli rested for Tuesday's visit of Liverpool to Eastlands, Mancini had to look on as his players struggled to break through the Sunderland defence.
City spent much of the second period camped in Sunderland's half and Micah Richards headed against the crossbar in the closing stages for the title contenders.
But Sunderland, who have lost just one of their opening five matches under new manager Martin O'Neill, then struck through Ji to make it a perfect start to 2012 for the north-east club.
Sunderland fans had every reason to fear the worst because O'Neill was forced to name two central midfielders in the full-back roles.
In the absence of the injured Titus Bramble, Phil Bardsley and Kieran Richardson, Craig Gardner and Jack Colback were the men charged with keeping Adam Johnson and Samir Nasri quiet.
Added to that there was a surprise recall for goalkeeper Simon Mignolet, sporting a mask to protect the fractured nose and eye-socket he sustained back in October, because of an injury to Keiren Westwood.
Yet Sunderland, despite their problems, should have taken an early lead.
When an early Johnson corner broke down, Sunderland found themselves in a fantastic position. Stephane Sessegnon turned inside his own half before rolling Nicklas Bendtner in behind the visitors' defence.
The Denmark international only had Joe Hart to beat, but the England goalkeeper got down low to prevent Sunderland taking an unlikely lead.
Sunderland's cause was not helped by the early withdrawal of Wes Brown, with Matt Kilgallon asked to keep the City attacks at bay in his first Premier League outing in 18 months.
That did lead to an increase in attacking play from City. Yet a combination of Mignolet, who denied Edin Dzeko from close range, and Gardner, who cleared a Nasri drive off the line, kept the visitors at bay.
It was an indication of City's frustration that both Aguero and David Silva had been introduced inside nine minutes of the second half -- and that lifted Mancini's men.
And when Silva linked with Dzeko after Aleksander Kolarov had got away with a shove on Sessegnon, Aguero's instinctive shot had to be turned away by Mignolet.
Mancini barked out the orders from the line in the hope of a late winner -- and one very nearly arrived in the dying stages.
When Silva's shot was denied by Mignolet, the rebound looked to have fallen kindly for Richards, but the defender's header cannoned off the bar and Gardner cleared.
And with literally seconds remaining, Sunderland broke away through the lively Sessegnon. He played in Ji and the South Korean rounded Hart to slot in the unlikely winner.