A David Raya penalty save sparked a rapid turnaround at the Stadium of Light, leading to goals from Bruno Guimaraes and Bukayo Saka to keep the Gunners atop the table.
A rejuvenated partnership between Kai Havertz and Martin Ødegaard overturned an early deficit to keep Mikel Arteta's side level with Manchester City at the top.
The transfer represents pure profit for Arsenal, who have overhauled their attack following the departures of Martinelli, Gabriel Jesus, and Leandro Trossard.
As Manchester City matched the British transfer record for Enzo Fernández, Arsenal opted for internal solutions after a quiet transfer window.
Bolstered by squad continuity and new midfield additions, Arsenal enters the new campaign as the overwhelming favorite among experts despite widespread managerial changes across the league.
Mikel Arteta and Enzo Maresca navigate major squad absences and late transfer dealings as Arsenal and Manchester City meet in Cardiff for the Community Shield.
Mikel Arteta is personally leading Arsenal's pursuit of the Brazilian forward as Real Madrid president Florentino Pérez refuses to break the club's salary hierarchy.
Arsenal have emerged as contenders to sign Real Madrid forward Vinícius Júnior after making an initial inquiry for the Brazil international.
Arsenal have completed the £34 million transfer of winger Christos Tzolis from Club Brugge to replace the departing Leandro Trossard.