Riccardo Calafiori scored the only goal after the Italian defender pounced on a huge mistake by United's stand-in goalkeeper Altay Bayindir. United have splashed out £200 million on new forwards to remedy a lack of punch in the final third.
Despite promising debuts, Matheus Cunha and Bryan Mbeumo failed to find the net, while substitute Benjamin Sesko could not make Arsenal pay for not pursuing their interest in the Slovenian. After finishing second for the past three seasons, the pressure is on Arsenal boss Mikel Arteta.
The Spaniard was left to depend on his reliable defence and goalkeeper David Raya as the visitors never got going as an attacking force. Only four other teams scored fewer than United's 44 goals in 38 Premier League games last season as the English giants just started new season in the way they had done the previous one.