Arsenal handed the initiative in the race for Champions League qualification to rivals Tottenham as Brighton ended their own dire run of form with a deserved win at Emirates Stadium.
The Seagulls - seven games without a victory before kick-off - frustrated the home side with their organisation and efficient forward play in a game where Arsenal failed to look threatening until they mustered a desperate late push.
Leandro Trossard's curling first-half finish - after a fine assist by the impressive Enock Mwepu - gave Graham Potter's side something to build on.
And after Gabriel Martinelli appeared to have headed Arsenal level moments before the break - only for a four-minute VAR check to rule him offside - Brighton remained solid before doubling their lead with a superb Mwepu finish.