Zlatan Ibrahimovic’s talismanic powers proved invaluable to Jose Mourinho and Manchester United once more as his introduction as a second half substitute helped inspire them to a 1-0 victory over Brighton.
Ashley Young was the scorer, with an 18-yard shot that took a cruel deflection via defender Lewis Dunk from a cleared Marcus Rashford corner after 66 minutes.
And Brighton, who gave an impressive account of themselves on their first ever Premier League visit to Old Trafford, were furious that the corner award went against defender Solomon March in the first place.
But lacklustre United had required the added impetus offered by Ibrahimovic who had been brought on just four minutes earlier as a replacement for the ineffective Juan Mata.
United had taken until the 45th minute even to test Mat (CORR) Ryan for the first time, with the Brighton goalkeeper proving well up to the task as he made a magnificent double save on his goal line from a Romelu Lukaku header and follow-up effort from Paul Pogba following Rashford’s far-post cross.
But that was the first time Chris Houghton’s side had looked remotely troubled during an impressive first half display.
Indeed, the best chances of the opening exchanges were carved out by the newly-promoted visitors, sitting proudly in the top 10 of the Premier League table before kick-off.
Just three minutes had gone when the lively Anthony Knockaert sprinted to the by-line and sent over a dangerous cross which just eluded team mates Glenn Murray and March in the six-yard area.
Then twice in quick succession David De Gea was called into action, making what turned out to be routine saves to gather shots from Pascal Gross and Knockaert.
It was probably not the script or the approach United had expected from a newly-promoted visitor, as they looked to cut rivals Manchester City’s lead at the top of the table to five points.
After two minutes, Lukaku had played a neat one-two with Anthony Martial, only to undo the good work by leaning back and shooting high over the Brighton goal.
A well-aimed Martial cross from the left almost set up another chance for the Belgian striker but Ryan rose well to collect and, in their attempts to get Lukaku more involved, Mata’s 24th minute cross picked out his team mate but he was unable to put any power into his headed effort.
It took until the 33rd minute for United to force so much as a corner and, a couple of minutes later, when Antonio Valencia crossed promisingly from the right, it was predictable that Lukaku could only head wide inside a crowded six-yard box.
In fact, Brighton again looked the more likely to score when Gross’s free-kick was flicked on and Murray flung himself, narrowly missing contact with what would have been a spectacular diving header on goal.
The visitors retained a strong foothold in the game after the restart, with Murray coming close to making telling contact on Gross’s cross and Davy Propper shooting over from 25 yards.
United responded, with Juan Mata shooting directly at Ryan, Lukakau almost playing in Pogba with a back heel and Ashley Young planting a left-foot shot wide.
But, by the 62nd minute, Mourinho had seen enough and brought on Ibrahimovic who won a corner with his first touch and instantly raised the atmosphere at Old Trafford with the opening goal coming just four minutes later.
Still, Brighton were undaunted with Dunk leading a breakaway charge upfield before flicking a weak shot at De Gea and Knockaert sending over yet another dangerous low cross-shot which passed just beyond the far post.
In the closing stages, Shane Duffy almost met a far-post set-piece and Ibrahimovic had two shots on goal without managing to test Ryan.
Manchester United (4-2-3-1): De Gea 6; Valencia 6, Lindelof 7, Smalling 6, Young 7; Pogba 7, Matic 6; Mata 5 (Ibrahimovic 62, 8), Rashford 5 (Fellaini 79, 6), Martial 5 (Mkhitaryan 70, 6); Lukaku 6. Subs (not used) Rojo, Romero, Herrera, McTominay
Referee: N Swarbrick 7