United wasted little time stamping their authority on the game as strikes from Mason Greenwood and Bruno Fernandes put them two up before the half-hour mark.
Greenwood was the provider for Fernandes' second after 50 minutes as Ole Gunnar Solskjaer's side made it eight games unbeaten in the Premier League.
The result moved United up to fifth, two points behind Chelsea, although they have played a game more. Brighton, meanwhile, remained in 15th, six points above the relegation zone.
United started on the front foot, with Fernandes crashing a long-range effort against the post after 12 minutes.
They did not have to wait long to open the scoring, though, Greenwood surging into the penalty area, bamboozling Lewis Dunk with a series of stepovers and clipping a smart finish past Mat Ryan at his near post in the 16th minute.
That advantage was doubled in the 29th minute when Fernandes' strike from 20 yards took a wicked deflection off Alexis Mac Allister to wrongfoot Ryan.
A devastating counter attack led to United's third five minutes after the restart, Greenwood picking out Fernandes at the back post with a sumptuous cross, with the Portuguese volleying past a helpless Ryan from eight yards.
Substitute Leandro Trossard twice flashed efforts wide after the hour mark, while David de Gea tipped over Aaron Connolly's strike as Brighton belatedly woke from their slumber.
Graham Potter's men failed to score a consolation, though, as United strolled to the most comfortable of away wins.
What does it mean? New-look United taking shape
Big things were expected from Fernandes when he joined from Sporting CP in January and he has not disappointed. Not only has he proven to be a potent goal threat – his brace took his tally to five goals in eight Premier League games – but he has elevated those around him.
United have been insipid in attack for so long but with Fernandes conducting an exciting forward line, fans might dare to dream of a title push in the coming seasons.
Greenwood continues to sparkle
The 18-year-old has enjoyed a superb breakout season for United and once again showed why he is such an exciting talent. It is testament to his prodigious ability that he slots in so seamlessly alongside seasoned internationals like Paul Pogba, Marcus Rashford and Fernandes.
Lewis slam Dunk-ed by Reds
The Seagulls captain endured a game to forget. He offered little resistance to Greenwood for United's first and failed to effectively marshal his defence throughout.
Key Opta Facts
- United extended their unbeaten run to 15 matches across all competitions (W11 D4); only Bayern Munich (25 games) are currently on a longer such streak without defeat among all sides in Europe’s big-five leagues.
- Brighton have won fewer Premier League games in 2020 than any other side (P13 W1 D7 L5).
- United have kept more clean sheets in their last 13 league games (eight) than they managed in their first 40 under manager Solskjær (seven).
- Greenwood's six goals for Man Utd in 2019-20 is the most by a player aged 18 or younger in a single Premier League season since Wayne Rooney scored nine for Everton in 2003-04.
- Since his debut in February, Fernandes has been directly involved in more goals in all competitions than any other Premier League player (10 - six goals, four assists).
- Fernandes has been directly involved in eight goals in his first eight league games for Man Utd (five goals, three assists) - only Robin van Persie has had more goal involvements (nine) after as many games at the start of his Premier League career with the club.
United will be confident of securing a third consecutive Premier League win when a struggling Bournemouth visit Old Trafford on Saturday, while Brighton travel to Norwich City on the same day.