Ansu Fati and Simon Adingra got a goal and an assist each as a clinical Brighton side stunned Ajax 2-0 in Amsterdam to move into the qualification spots of their Europa League group for the first time.
Ashley Young's 84th-minute own goal rescued a point for Brighton as Everton were denied back-to-back Premier League victories in a 1-1 draw at Goodison Park.
Brighton's eagerly awaited European bow fell flat as Greek heavyweights AEK Athens stunned Roberto de Zerbi's men with a 3-2 Europa League group stage victory.
Luton scored twice inside the opening three minutes and Elijah Adebayo claimed a hat-trick in a remarkable victory over Brighton which lifted the Hatters out of the Premier League relegation zone.
Substitute Kaoru Mitoma's second-half double helped Brighton come from behind to beat winless Bournemouth.The Japan midfielder scored 16 seconds after coming on, then headed in later to clinch a third straight Premier League win.
Chelsea have finally agreed a fee with Brighton for defender Marc Cucurella, though the Blues have had to commit to a transfer package that could reach £63million.
Former Man Utd striker Danny Welbeck opened the scoring for Brighton; Pascal Gross and Joao Pedro added second-half goals after poor defending; Hannibal Mejbri replied for Man Utd; hosts have now lost three of their opening five Premier League
First-half goals from Julian Alvarez and Erling Haaland give Manchester City a 2-1 win over Brighton to end a run of three domestic defeats; Ansu Fati reduces arrears for Seagulls but they cannot find leveler despite Manuel Akanji's late red