Andreas Pereira and Davy Propper, in their own door, were the scorers of the meeting in Old Trafford in the first half, on a quiet afternoon for the 'Red Devils'.
He was only about to twist when Lewis Dunk cut distances in the 64th minute, but United, far from getting nervous at the push of the 'Seagulls', responded through Marcus Rashford.
Just two minutes after Dunk's goal, Rashford signed the third and sentenced the match, although Ole Gunnar Solskjaer's men were able to increase the rent.
It is the second consecutive win of United, which could already last Thursday in the Europa League with the Partizan of Belgrade, which also endorsed three goals.
The victory means that United climbs to seventh place, with 16 points, one from Sheffield United, which marks the Europam League positions and nine from Manchester City, which is fourth in Champions League positions.
The Brighton is eleventh with 15 points, seven above the relegation positions.
Also this Sunday, before the game between Liverpool and Manchester City, Wolverhampton Wanderers beat Aston Villa 1-0. EFE