Ashley Young's deflected strike proved the slice of luck Manchester United needed to sneak past promoted Brighton.
Swashbuckling Manchester City headed into the weekend with an eight-point cushion at the top of the Premier League, and that meant Jose Mourinho's second-placed side could ill-afford to drop points at home to Chris Hughton's men.
Well-drilled Brighton threatened to cause an upset as they impressed on their first trip to Old Trafford since 1993, only for Young's strike to loop in via a cruel deflection off Lewis Dunk as United eked out a 1-0 win.
It took their run of victories at home against Premier League newcomers to 19 matches, getting an important sequence of games off to a winning start ahead of trips to Watford and Arsenal.
Brighton were unlucky to see their five-match unbeaten run come to an end after an assured display at Old Trafford, where they panicked the hosts with fleet-footed counter-attacks and dangerous crosses.
Their goalkeeper Mathew Ryan produced a fine double-save to keep United from grabbing the lead just before half-time, but the Australian could do nothing to prevent Young's second-half strike flying off Dunk and past him.
It was a welcome return to winning ways for United after their midweek Champions League loss in Basel, but Mourinho's pre-match call for his players to begin sharply fell on deaf ears.
Romelu Lukaku's wayward strike set the tone for a plodding first half against a confident Brighton side, with Anthony Knockaert's fizzing cross a fourth-minute shot across the bows before David De Gea comfortably stopped Pascal Gross' first-time attempt.
United were struggling to create clear-cut chances and Lukaku was unable to direct headers on target when the odd cross found the targetman. At the other end, Albion's figurehead Glenn Murray was inches away from connecting with a flick-on from close range.
As impressive as the Seagulls were, Ryan had to be his best to prevent them falling behind just before half-time.
Brighton's goalkeeper did superbly to get in the way of a point-blank Lukaku header, with the Australia international quickly reacting to prevent the follow-up as Paul Pogba attempted to slot home.
But the chance, and Mourinho's half-time team talk, did not jolt United into life as the second period started with Gross fooling Chris Smalling to send over a tantalising cross, before Davy Propper tried his luck from distance.
United continued to bumble along in attack as Lukaku tried a back-heel and Young smashed wide, with it taking a crunching Victor Lindelof challenge on Knockaert to get the fans roaring.
Mourinho's men refused to give the ball back despite the winger lying on the deck, with chants of "attack, attack, attack" echoing around Old Trafford.
Zlatan Ibrahimovic was introduced as United began to ratchet up the pressure and it bore fruit in the 66th minute.
From a disputed corner, left-back Young tried his luck from the edge of the box, with his effort taking a huge deflection off Dunk and looping into the top corner.
Lukaku tried to quickly extend United's lead but the visitors were not cowed and continued to attack, with Bruno's wonderful cross evading team-mates, and Shane Duffy just unable to reach a ball into the box. Ibrahimovic got away an attempt as the home side secured victory.