Arsenal scored twice in stoppage time to secure a dramatic victory over Manchester United at Emirates Stadium.
In a chaotic finale to a largely scrappy game, United first thought they had snatched three points only to see Alejandro Garnacho's 88th-minute finish ruled out for offside by the video assistant referee with the score 1-1.
The drama then switched to the other end in eight added minutes as Declan Rice's deflected shot gave Arsenal the lead before substitute Gabriel Jesus raced clear to wrap up the win as the stadium exploded in elation.
United had taken the lead in the 27th minute when Christian Eriksen's outstanding pass played in Marcus Rashford, who cut inside to send an unerring right-foot drive past Arsenal keeper Aaron Ramsdale.
The Gunners, who had already spurned a golden chance when the struggling Kai Havertz miskicked with the goal at his mercy, were level almost instantly when captain Martin Odegaard was given too much space and sent an emphatic finish into the bottom corner.
In an encounter that rarely hit the heights despite lots of effort, Arsenal - who had seen a penalty over-turned by the VAR after referee Anthony Taylor originally ruled Havertz had been fouled - missed a glorious late opportunity when Bukayo Saka shot straight at Andre Onana.
United saw celebrations cut short with two minutes left when substitute Garnacho raced clear to score, but the VAR ruled he was just offside - opening the door for Arsenal to produce two devastating blows.
Arsenal's late show brings vital win
Arsenal put their fans through the emotional wringer before sheer joy swept around Emirates Stadium at the sound of Taylor's final whistle.
For most of this match, the hosts could not find the pace and fluency that made them such an attractive, winning proposition last season as there was simply too much tension around their play.
Havertz continues to look an expensive luxury item, his role in the Gunners set a mysterious one, but when it mattered Mikel Arteta's side raised themselves to deliver a vital win when it looked like they would drop points for a second successive home game after being held by Fulham.
For a few moments it looked like defeat would be Arsenal's fate until VAR ruled Garnacho had gone just too soon before beating Ramsdale with a composed finish.
Rice deserved his goal, albeit one deflected off Jonny Evans at the near post, for an outstanding individual display that illustrated once again why Arteta made his £105m signing his main summer priority.
And then Jesus showed what value he brings to Arsenal when, with United chasing an equaliser after being stunned by Rice's goal, he embarked on a weaving solo run before beating Onana.
It means Arsenal are still in touch with Manchester City and there is a real feeling of optimism going into the international break.
United suffer sucker punches
Manchester United went from believing they had fashioned a statement win at Arsenal to drooping off with heads bowed after being floored by two late sucker punches.
The anxious glances as United's players and staff waited for the VAR verdict on Garnacho's strike were followed by the disappointment of seeing it ruled out then the despair of the late surge that brought the Gunners victory.
It brought more disappointment for United in north London after their defeat at Tottenham although there was some hope in a bustling cameo debut from £72m striker Rasmus Hojlund, who looks like he might at least give their attack some physical presence and a focal point.
The visitors were disappointing in creative areas despite Rashford's superb goal, and it is a sign of how reduced they are in defence that they ended the game with Harry Maguire, effectively cast out by manager Erik ten Hag, and 35-year-old emergency signing Jonny Evans trying to keep Arsenal at bay.
In reality, this has been a stuttering, unimpressive start to the season by United - now Ten Hag must hope the international break gives him time to get his side into gear for when they face in-form Brighton at Old Trafford in their next Premier League game.