Arsenal suffered their first defeat of the season after Brighton beat them 3-0 at the Amex Stadium on Saturday.
The Gunners struggled to find their rhythm as Brighton took control of the game early on.
Pascal Gross opened the scoring in the 31st minute with a long range effort that found the net after hitting the post.
Arsenal came close to an equaliser before the break when Bukayo Saka had a good opportunity, but Brighton goalkeeper Bart Verbruggen made the save.
Brighton quickly punished Arsenal for the missed chance. Charalampos Kostoulas doubled the lead just before half time with another strike from outside the box.
Arsenal needed a strong response after the break but Brighton remained in control.
Chema Andres made it 3-0 in the 57th minute when he headed home from Gross’s corner.
The result brought Arsenal’s perfect start to the season to an end. The defending champions had won their opening league matches and all seven of their games in all competitions before Saturday’s defeat.
Brighton also continued their strong run after recent victories over Coventry City and Manchester United.
Arsenal will now look to bounce back when the Premier League returns.