Paul Pogba started in his return from his hamstring injury and put in a strong performance, creating one goal and scoring another.
Anthony Martial, Chris Smalling and Romelu Lukaku added the other goals for the Red Devils, and Zlatan Ibrahimović made a late cameo in his first appearance since tearing his ACL last spring - but what can United take away from the win?
No-one can overstate Pogba's importance
Much has been said and written about how much United have struggled without Pogba this season.
The UEFA Super Cup loss against Real Madrid notwithstanding, United are unbeaten with Pogba in the starting XI this season.
Without him, they lost to Huddersfield Town as well as Chelsea, their only league defeats this term. However, his absence did not just hurt the Reds in terms of results.
Without the Frenchman on the field, United looked slow, incapable of putting supposedly weaker teams consistently on the back foot.
Pogba has a unique ability to put his foot on the ball, and dictate the entire flow of the game. He can hold off a defender in almost any situation, which creates time and space for those around him. It helps relieve pressure on his teammates, and better retain possession.
His attacking ability was on show for all to see on Saturday, and there were few more impressive pieces of skill than his stop-and-go to create space for his assist on Martial's goal.
Simply, United are a different team with Pogba healthy. To have a chance at catching Manchester City, they need him at his best.
Squad depth returning at crucial time for Manchester United
Over the last month, United have struggled with a plethora of injuries.
At the same time Henrikh Mkhitaryan lost form, Pogba and Marouane Fellaini went down injured. Marcos Rojo and Ibrahimović were both working to get back from long-term injuries.
Club captain Michael Carrick is still stuck on the sidelines. Thus, United manager José Mourinho's team selections were constrained, and United hadn't managed to score more than two goals in a game since September.
Now, as they head towards the festive fixture period, United are at almost full-strength. Pogba and Fellaini's return to fitness mean that Nemanja Matić need not play all 90 minutes of every game.
Ibrahimović can spell Lukaku, or provide a Plan B off the bench should United fail to unlock a defence in the first three-quarters of a game.
From the time the Reds take the field against Basel on Wednesday to New Year's Day, United will have to navigate 13 games in the space of 41 days.
Every team struggles in that period but having so many key players return at once puts United in the best possible position to take advantage of any stumbles from other title challengers.
Newcastle could be building something special
The Magpies did not have a particularly impressive performance on Saturday.
While they started well, and Gayle's goal capped a superb attacking move, they wound up well-beaten by superior opposition. That said, this team has shown flashes of terrific play.
They sit 11th in the table, and ought to stay up comfortably. In Rafa Benítez, the club have the absolute right manager.
Should Mike Ashley actually sell to someone that would be willing to sink significant funds into building up the squad, Newcastle might not be too far away from another charge at European football.
Martial and Rashford can play at the same time
United set up in a 4-2-3-1 formation, which meant that Mourinho could accommodate both Martial and Rashford in the starting eleven.
Newcastle couldn't neutralise the threat both offered running with the ball at their feet, and each was a danger throughout the game. Martial took his goal well, and Rashford did brilliantly to create Pogba's goal.
The end product provided more than made up for the fact that each was culpable of giving the ball away cheaply and occasionally held onto it for too long.
That's part of offering young players a chance to play. These two are both so talented and have all the potential in the world. All season long, Mourinho has treated them as like-for-like substitutes.
On Saturday, he left behind his aversion to starting them together, and each clearly had the license to take people on and look to create for themselves and for teammates.
There will be games this season where they can't both start, either because Lukaku and Ibrahimović need to play next to each other or an extra midfielder needs to come into the middle of the park.
However, it's clear that when the occasion calls for it, Rashford and Martial offer a dangerous two-pronged attack on either flank.
The title is City's to lose
United put in a strong performance on Saturday and were good value for their victory.
Tottenham's loss at Arsenal clarified that each member of the Premier League's big-six will chase the European places at least, if not maintain some semblance of a title challenge through the coming months.
However, City's comfortable victory over Leicester City leaves them eight points ahead of United in second, while the gap from second to sixth in the league is just four points.
It's entirely likely that the chasing pack will take points off of each in the weeks and months ahead. City have already built up the kind of cushion that can weather a brief loss of form.
The fate of the league is in their hands, no matter what any other team might want to think.