Aaron Ramsey scored twice as Arsenal beat bottom club Sunderland, who had boss Paolo Di Canio sent off.
Arsenal debutant Mesut Ozil set up Olivier Giroud for an early strike, with Craig Gardner equalising from the spot after the break.
But after Ramsey volleyed in, Di Canio was infuriated when Jozy Altidore was denied a leveller after referee Martin Atkinson failed to play an advantage.
Ramsey scored a fine second as Arsenal moved to the Premier League summit.
The result was their fifth consecutive win after losing on the opening day to Aston Villa.
The hosts were fortunate to still be in the game at the break as Ozil made an instant impression following his £42.5m move from Real Madrid by demanding the ball early on and providing a host of chances.
Theo Walcott could easily have had a hat-trick before the break but found Sunderland goalkeeper Keiren Westwood in impressive form, as he twice denied the England winger after he was set clear by Jack Wilshere and Ozil.
Altidore's disallowed goal then cast a defining narrative in the match and once Ramsey tucked in after a sweet pass from Giroud for his fifth of the season, Sunderland could not find a way back.