The result brings Arsenal's unbeaten league run to an end and also snaps a seven-game winning streak in all competitions.
Arsenal have suffered their first Premier League defeat of the season after a 3-0 loss away to Brighton.
The champions were two goals down by half-time following strikes from Pascal Gross and Charalampos Kostoulas, before Chema Andres added a third early in the second half.
The result brings Arsenal's unbeaten league run to an end and also snaps a seven-game winning streak in all competitions.
Manager Mikel Arteta said afterwards that Brighton were the better side and admitted his team fell short in key areas, particularly in duels, second balls and possession.
Brighton's victory is one of their biggest results of the season so far, while Arsenal will now look to respond quickly after their first major setback of the campaign.

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