Ole Gunnar Solksjaer has become the first Manchester United manager in history to win his opening six league games in charge.
United's two first-half goals were too much for Brighton, despite an attempted fight back in the second-half.
Paul Pogba won and then scored the penalty to put the Red Devils in front at Old Trafford, before Marcus Rashford scored a beautiful goal to mark his 150th appearance for United.
Pascal Gross offered a reply for Brighton, but Solksjaer's team held on to create history in Manchester.
Image via @PremierLeague on Twitter
Nemanja Matic found Pogba with a cross-field ball, and the France midfielder took it past Gaetan Bong, who then fouled him and it was a penalty.
Pogba took, with his stuttering penalty run-up, and gave the hosts a lead on 27 minutes.
Rashford's hot-form continued as he scored his ninth goal of the season when he was played in by Diogo Dalot and then curled his shot into the top corner.
The England forward's goal right on half-time sent the home team into the break with a comfortable two-goal cushion.
The second-half tempo slowed down considerably with Solksjaer trying to use his game management abilities to see out the match.
However, Brighton replied on 72 minutes through Gross, who chested down Davy Propper's cross brilliantly and smashed it past David de Gea.
Rashford came off towards the end of the match and the United forward got a standing ovation from the Old Trafford faithful after another tremendous performance.
United held on despite some late pressure from the Seagulls, and Solksjaer's perfect start continues.
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