Arsenal kept up their hopes of securing a place in the English Premier League top four on Sunday, and also ended Manchester United’s 25-match unbeaten run in the competition.
It was a match that was looking largely uneventful, until Granit Xhaka opened the scoring with a deflected shot from distance which looped over goalkeeper David de Gea.
Their fans were yet to get over the celebration of a likely win over a difficult opponent when Danny Welbeck doubled their lead three minutes later.
He headed home against his former club after a pinpoint cross from Alex Oxlade-Chamberlain.
Manchester United introduced Marcus Rashford and Jesse Lingard to try to rescue the game, but they failed to bring the visiting side to life.
The result means Arsenal remain in sixth place.
But they are two points off Manchester United in fifth and six points off Manchester City in fourth, with a game in hand over both teams.
The victory not only reignites Arsenal’s chase for a UEFA Champions League place, but also ends an unwanted record.
Arsenal manager Arsene Wenger and his Manchester United opposite Jose Mourinho have endured a fractious relationship over the years.
In their previous 15 competitive meetings, Wenger had never beaten a team led by Mourinho, with his only victory coming in the Community Shield in 2015.
Sunday’s win ended the hoodoo and earned Arsenal only their 13th league win in 50 outings against the Red Devils.
There is still uncertainty about Wenger’s future at the club, in spite of their still being in with a chance of Champions League football for the 21st consecutive season.
They also have an FA Cup final against Chelsea coming up this month.