Sunderland moved up to second place in the Premier League after handing Chelsea a 2-1 home defeat as substitute Chemsdine Talbi curled in a low shot deep into stoppage time on Saturday.
The visitors had gone behind in the fourth minute when Alejandro Garnacho claimed his first goal for Chelsea.
But the Londoners' lead was cancelled out by Wilson Isidor's equaliser in the 22nd minute as the Frenchman stabbed in from close range after Chelsea failed to deal with a long throw.
The game appeared to be heading for a draw before Talbi ran on to a pass by fellow substitute Brian Bobbey in the third minute of added time and left Robert Sanchez with no chance.
Back in the Premier League for the first time in eight years, the Black Cats already look set to buck the trend of promoted sides being relegated straight back to the Championship.
Chelsea looked like they would be the side to go second in the table when Garnacho drilled in his first goal for the club after just four minutes.
However, with Brazilian wonder kid Estevao surprisingly dropped to the bench and Cole Palmer still missing through injury, the Blues lacked conviction in the final third.
Sunderland levelled on 22 minutes when Isidor scored from close range.
The visitors comfortably held the Club World Cup winners at bay in the second period despite Estevao's introduction on the hour mark.
Sunderland then landed the sucker punch on the counter-attack in the 93rd minute when Brobbey teed up Tabli to curl perfectly into the bottom corner.
The defeat left Chelsea down in seventh and any hope of a title challenge fading fast.
Chelsea defender Trevoh Chalobah said the team need to learn from the defeat.
“Difficult one, they came to disrupt our game. We had a couple of chances in the first half, we created some in the second but switched of at the end. As a team it is not the best of games but it is one we have to learn from,” he told Sky Sports.
“With the Champions League we have a lot of games but we can't complain. These are the games we want to play in and we can't use that as an excuse.”
Sunderland coach Regis Le Bris said his players had found the right balance between pressing Chelsea high up the pitch in key moments before holding their deep blocking formation.
"It's a good performance, especially after the early goal," the Frenchman told reporters. "We won three points. We are happy with the way we played. It is important to grab this opportunity when possible."
Newcastle strike late
Newcastle United secured a much-needed league win thanks to captain Bruno Guimaraes' 90th minute strike that secured a 2-1 victory over Fulham at St. James' Park.
Jacob Murphy pounced on an error by Calvin Bassey to give the Magpies a first-half lead.
Sasa Lukic headed in Fulham's equaliser just before the hour mark.
But Marco Silva's men fell to a fourth consecutive defeat that leaves them hovering just above the relegation zone.
Guimaraes swept home the rebound after Bernd Leno had saved William Osula's initial effort to snatch just Newcastle's third league win of the season.
Eddie Howe's men climb to 11th and within three points of the top four.
