Nathan Redmond tapped home a cross from Sofiane Boufal to seal the points in injury time. Brighton played a man light for an hour after striker Florin Andone was sent off for a reckless tackle on Yan Valery, while Lewis Dunk had a first-half header ruled out by the video assistant referee.
Prior to Redmond's strike, Brighton pushed hard for an equalizer and struck the woodwork through substitute Jurgen Locadia before falling to a first defeat under new manager Graham Potter. Southampton had lost to Burnley and Liverpool this season.
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