Ashley Young's deflected second half cross ensured United of the three points and took the hosts' unbeaten record at home to 39 straight matches.
Making their first trip to Old Trafford in league play since 1983, the Seagulls never looked out of place in the first half. The visitors from the south coast went almost the entire first half unscathed by the attacking forces of the Red Devils, and Brighton looked extremely dangerous in the wide areas on the counter attack.
United had the first good chance at goal in the second minute, but Romelu Lukaku fired a shot 20 rows up into the East Stand.
Anthony Knockaert and Pascal Groß both had good chances on goal within the first twelve minutes, but the former’s chance went without conversion and Groß’s was a weak shot into the hands of David de Gea.
Anthony Martial had a penalty shout go unanswered in the 16th minute, a rare flare from United’s attack in the first part of the first half.
Glenn Murray almost put the Seagulls up a goal in the 39th minute, but his dive to reach a flick-on towards the back post was just short and the chance was squandered.
The best goal scoring chance from either side came just as the clock reached the 45th minute, as Lukaku and Paul Pogba had back to back chances saved spectacularly on the goal-line by Mathew Ryan. Pogba appeared to hurt his knee on the attempt but he walked it off and returned in injury time.
United and Brighton played a quiet first 20 minutes of the first half, with both sides finding it difficult to find space i the final third. The hosts, who had most of possession, failed to muster anything coming out of the locker-room.
Manchester United manager Jose Mourinho brought on Zlatan Ibrahimovic in the 62nd minute in place of Juan Mata, who failed to create much. The Swede slotted in just behind Lukkau in the number ten position.
United broke the deadlock in the 68th minute, when a deflected Ashley Young shot from outside the box looped over Ryan and into the back of the net. The shot, which came as a result of a cleared corner attempt, deflected off of Lewis Dunk and gave Ryan no chance in goal.
Albion will rue multiple opportunities they had on the counter attack, as the Seagulls failed to convert the final ball in the final third each time. Lewis Dunk was played in the 72nd minute but failed to pull the trigger and was disarmed by the United defense.
Brighton had two identical opportunities go unanswered in the 75th and 78th minute, when Knockaert and Bruno Saltor both whipped in balls across the six yard box but both times the great passes went untouched and the chances were lost.
The Seagulls’ Shane Duffy missed a chance for a header towards the back-post in the 86th minute, a chance on a free kick that looked primed to be the equalizer for the visitors.