Watch: Leandro Trossard stuns Arsenal with a sublime strike into the top corner
Brighton took the lead at the Emirates Stadium when Leandro Trossard turned home a low cross from Enock Mwepu to finish a good move from the visitors.
Arsenal had struggled to create chances but thought they had levelled through a close-range effort from Gabriel Martinelli, only for a lengthy VAR check to cancel out his header.
Advertisement
Hide AdAdvertisement
Hide AdArsenal named Granit Xhaka at left-back as they made two changes for the visit of Brighton.
The Gunners lost 3-0 at Crystal Palace on Monday night and the injured Thomas Partey was replaced by Albert Sambi Lokonga.
Nuno Tavares was hauled off at half-time at Selhurst Park and lost his place to Gabriel Martinelli as Xhaka filled in at full-back.
Brighton ended a six-game losing streak with a 0-0 draw at home to bottom club Norwich last weekend and Graham Potter's team started well.
Advertisement
Hide AdAdvertisement
Hide AdMoisés Caicedo impressed in the Albion midfield on his debut. The Ecuador international delivered a powerful and composed first half display.
Mwepu, who has had his injury troubles this season was also an influential figure and will hope to have a strong end to the season.
His return to fitness is a timely boost following the serious ACL injury sustained by Jakub Moder against Norwich.