It wasn't pretty and certainly wasn't vintage from United, but this could be a win as vital as any in the final reckoning come May.
Ashley Young scored his first 'goal' since the final league game of the 2015-16 season, but his heavily deflected strike will probably go down as a Lewis Dunk own goal.
United had breezed past another newly promoted team in Newcastle last time out, but this proved to be a much more testing examination against the south coast side.
The 4-1 win over the Magpies was the seventh time that United have scored four goals in a game this season, but you're not going to get that every week in this league.
The ability to 'win ugly' and grind out results is the true test of any side with lofty ambitions, and when your team can do so, it's often more satisfying as a fan than a comprehensive win.
That's exactly what United had to do here as we were frustrated for long periods by Chris
The visitors defended stoically, and had their moments going forward too but - in the end - United probably just about merited the win.
Brighton were dogged, determined and resilient, and the Seagulls showed all the endeavour and team spirit that sent them soaring from the Championship and into a first ever Premier League campaign.
On this showing, it will be enough to keep them there.
Jose praised the efforts of the visitors, and said that Brighton gave United our hardest game of the season - high praise indeed considering our recent away trips to Anfield and Stamford Bridge.
With unbeaten City the next league visitors to Old Trafford in a fortnight - after two away games at Watford and Arsenal - we'll need to produce a better performance than we showed here.
Romelu Lukaku looked flat throughout and his recent struggles in front of goal continued - but it was not for the want of trying though.
Having scored against Newcastle, he was only denied again here by the impressive reflexes of Brighton keeper Matt Ryan shortly before half -time.
It's been a season of feast followed by famine for our big Belgian striker - he scored eleven goals in his first ten games, but has now found the net only once in his last nine - and that came against Newcastle with the game won.
Paul Pogba completed the first 90 minutes since his comeback and Zlatan Ibrahimovic came on for the last half an hour as he continues his rehabilitation back up to full fitness.
United travel to Watford on Tuesday before arch rivals Arsene Wenger and Jose renew their bitter feud at the Emirates next weekend.
Then comes the small matter of that first Manchester derby at OT a week later, on December 10th.
City may have been picking up the plaudits for their thrilling style but there's more than one way to win a match and United have proved that substance can be just as important as style.
As the season enters its most pivotal point, you get the feeling there will be plenty of both as the Reds look to ramp up the pressure at the top.