The Gunners beat the Red Devils with two goals from set pieces by Timber and Saliba
They're not 'cannons', they're planes: Arsenal cause Amorim's first defeat with Manchester United

The 500th match in the history of the Emirates Stadium, which opened in 2006, will not go down in history. At least not for its beauty. Arsenal-Manchester United (2-0) was nothing like the late 20th and early 21st centuries duels, with Wenger and Ferguson in the trenches.
Amorim surprised everyone in his fourth game in charge with six changes! Lisandro, Diallo, Mainoo, Casemiro, Rashford, and Zirkzee made way for Maguire, Ugarte, Mount, Garnacho, Hojlund, and Malacia. Special mention goes to the latter, who made his return to the Premier League 546 days later!!!
Arsenal, without White, Magalhaes, and Calafiori in defense and Mikel Merino (substitute), were on the verge of taking the lead (almost) before the start. Not even three minutes had passed when Samuel Barrott disallowed Martinelli’s goal for offside.
It was a mirage. Both the Gunners and the Red Devils were more concerned with creating mistakes for their opponents than generating their own successes. Only set pieces broke the monotony.
Every corner was a nightmare for United. Thomas Partey headed a Rice corner wide of goal. He headed it in with his shoulder. Martinelli also came close to making it 1-0 in the 25th minute with a shot that went just wide of the top corner after another set piece.
United went into the break without a shot on target but almost took the lead when Diogo Dalot’s shot just missed the post in the 42nd minute.
Amorim brought on Diallo for Malacia to give him more of a presence in attack… but he didn’t succeed. On the contrary. Jurrien Timber ‘opened the scoring’ from a corner, of course. The former Ajax player headed in an extraordinary Rice cross at the near post to make his debut as a goalscorer for the ‘gunners’.