City is now runaway leader on 31 points, with United and Spurs, who beat Crystal Palace 1-0, trailing on 23 points, while Chelsea is fourth with 22, followed by Liverpool and Arsenal on 19.
Pep Guardiola's troops took their goals tally in all competitions so far this season to 52 as Kevin De Bruyne, Sergio Aguero and substitute Gabriel Jesus ensured a ninth successive league win.
City was not at its electrifying best against Arsenal but still had too much for Arsene Wenger's side.