United edged past the challenge of brave newly promoted Brighton through Ashley Young's fortuitous second half winner to extend our unbeaten home run to a 39th game.
The Reds were stifled by Chris Hughton's Seagulls for over an hour, until Young's 25-yarder hit Lewis Dunk and looped over Matt Ryan to earn United an eighth successive Old Trafford win.
The strike will probably go down as a Dunk own goal - but that would be very harsh on the Albion centre-back who had an otherwise excellent game at the heart of their defence.
United started strongly and went close inside the opening ten minutes, when Romelu Lukaku fired over the bar after neat link-up play with Anthony Martial.
Brighton arrived at Old Trafford on a five-match unbeaten run and in the top half of the table after a very steady start to their first ever Premier League season.
Pascal Gross tested David de Gea with a 20-yarder while last year's Championship Player of the Year Anthony Knockaert flashed an effort across goal that evaded everyone.
Glenn Murray failed to get on the end of a set-piece, but, just before half-time, Albion were indebted to their efforts of their Australian international keeper.
Ryan kept out Lukaku's point-blank range header with his foot, before he then somehow superbly denied Paul Pogba on the rebound when the Frenchman looked certain to score.
Following a half of frustration, the second period came to life after Victor Lindelof's crunching - but fair - challenge on Knockaert.
Zlatan Ibrahimovic then stepped off the bench on the hour mark, and United finally found the breakthrough six minutes after his arrival - albeit in a fortunate manner.
A corner, awarded when Lukaku and Duffy were involved in a coming together and disputed by Brighton, fell to Young and his speculative shot from distance struck Dunk on the knee and looped over the back-pedalling Ryan.
Knockaert went close when he fired across goal again, and Bruno Salter did likewise moments later as Brighton mounted a late push for a leveller, even though David de Gea had little to do.
Ibra almost put the result beyond doubt late on when he volleyed wide after superb link-up between himself, Lukaku and Pogba.
The result means United are now unbeaten at Old Trafford in 39 matches across all competitions, with our last home loss a 2-1 defeat to Manchester City in September 2016.
Next up at OT in the league? Yep, you've got it.... that lot from over the road on December 10th.
United Faithful Man of the Match: Victor Lindelof. THAT tackle on Knockaert alone makes him worthy of the MOTM award
Overall team performance: 6.5/10