Plenty needed to fall Brighton’s way if they were to breach the top six on the final day, yet a controlled start in the searing heat showed they were confident of holding up their end of the bargain.
Creating chances was tough in the face of a stubborn United backline, with the hosts’ most threatening moment of the opening 20 minutes coming when Maxim De Cuyper cut in from the left and curled just wide of the far post.
United took until the 33rd minute to register a shot, but they made it count and broke the deadlock.
Patrick Dorgu’s return to the starting XI for the first time since January was greeted by a third goal in as many starts from the Dane, who headed in Fernandes’ corner via the underside of the bar to take the Red Devils captain to 21 Premier League assists this term - an outright all-time competition record.
The momentum of the game completely swung on that goal, with the visitors going close to an immediate second when Luke Shaw whistled an effort just wide of the target.
Fabian Hurzeler’s men never really recovered despite surviving that scare, and were undone again in some style on the stroke of half-time.
Amad Diallo fed Mason Mount, who returned the favour by slotting the Ivorian in down the inside right, and he duly squared for Bryan Mbeumo to tap in his second goal in as many matches, with that also a career-high ninth Premier League goal involvement for the Cameroonian against Brighton.
The Seagulls were jeered off at the break, and the home fans’ mood only worsened after the restart.
Dorgu beat the offside trap to receive Amad’s pass, and teed up the overlapping Fernandes to rifle home United’s third of the afternoon.
Brighton were shell-shocked, and only a trio of smart saves from Bart Verbruggen prevented the rampaging Dorgu and Amad from further stretching the visitors’ lead.
While Diego Gomez directed a low effort wide, the Seagulls never really threatened Senne Lammens on a very disappointing afternoon.
Two successive losses without reply consign Brighton to the UEFA Conference League next season, with this just a third defeat in nine Premier League meetings with the visitors.
United, meanwhile, saw Leny Yoro hit the bar late on as they went into the summer on the back of five victories in six outings and a 24th win on the final day - only Arsenal have managed more in league history.