Noah Okafor’s double was enough to earn the Whites a famous victory against their bitter rivaks and pull six points clear of the drop zone.
It was the Yorkshire club’s first league win at Old Trafford since 1981 and only their second away triumph this season.
Few gave Leeds a chance against Michael Carrick’s side who have propelled themselves into a Champions League slot behind Arsenal and Manchester City. However, the visitors, missing key injured duo Joe Rodon and Anton Stach, turned in one of their best displays of Daniel Farke’s reign.
Their first-half performance was outstanding, full of skill, power, pace and control. From the first minute they were on the front foot, goalkeeper Senne Lammens blocking a close range effort from Dominic Calvert-Lewin after Gabriel Gudmundsson’s excellent low cross from the right.
The Red Devils were being passed off the park with their defence all at sea as Leeds oozed such confidence that it was hard to believe they had not won any of their last six league games.
Okafor’s instant shot after the ball skimmed off Lenny Yoro’s head gave Leeds a fifth-minute lead. The home side could not find a reaction as Farke’s men doubled their advantage just before the half-hour when Okafor’s volley nicked off Yoro beyond Lammens.
Old Trafford was stunned – apart from the 3,000 fans bouncing in the away end. It could have been even better but for a brilliant goal-line clearance by Lisandro Martinez to deny the Ao Tanaka a third Leeds goal.
It should have been straightforward for the Whites when Martinez was red-carded on 54 minutes for pulling Calvert-Lewin’s hair after a VAR review.
Instead. Leeds made life difficult for themselves. The home side played better with ten men than eleven, opting to go long towards big striker Benjamin Sesko.
Leeds no longer looked comfortable. Bruno Fernandes, the heartbeat of the home side, delivered a great cross for Casemiro to head in on 68 minutes.
Sesko was denied twice in a minute from goalkeeper Karl Darlow and then a goal-line clearance by Calvert-Lewin's.
Leeds, who also had second-half opportunities themselves on the break, rode out the storm to inflict Carrick’s first home defeat since taking temporary charge of the Old Trafford hot seat.
The victory was celebrated wildly by Farke and his staff on the touchline. They know if they beat bottom club Wolves at Elland Road on Saturday they will go nine points clear of danger before the other relegation candidates play.
A delighted Farke said: “We are in the crunch time of the season and it’s important to keep your nerves and stick to your plan.
“We were brave in our pressing in the first half. We could have easily been three or four goals up. We are not the finished end product and we can make a mistake. There’s no doubt we deserved to win.”