It was often a tense game at the Tottenham Hotspur Stadium on Saturday, but when Manchester United's superstars found the goal, Spurs never really looked like coming back.
There were boos for the home team's performance as the final whistle went, with the scoreboard showing 0-3.
Cristiano Ronaldo and Edinson Cavani displayed their class, even at advancing years, with two excellent finishes, and then Rashford came on to follow suit.
At the other end, Tottenham number 10 Harry Kane still looks off the pace.
The match was seen as big game for both managers, with Ole Gunnar Solskjær's job under threat and Nuno Espírito Santo yet to prove to Spurs fans that he's the man for the job.
In truth, this match may not change either's standing substantially.
The first effort on goal came five minutes in with a Son shot deflected wide, but United grew into the game, a header from Cavani flashing wide and a spell of protracted pressure.
A tame free kick from Lo Celso rebounded off the wall but the best chance of the game so far came with Son controlling a ball into the box before putting the shot over.
At the other end, a Cavani header again flashed wide.
On 27 minutes the ball was in the net, but a slow flag correctly called Romero offside.
United's most threatening moment so far came on 32 minutes with Lloris saving well from Fred.
Minutes later, Son looked sure to score, bursting through, one-on-on against the goalkeeper, only for Wan-Bissaka to make an outstanding tackle from nowhere.
The opening goal was provided by Ronaldo, beautifully placing a volley from a diagonal ball low into the corner.
At the start of the second half Son fizzed a glorious shot just wide before Ronaldo put the ball in the net at the other end, only to be called offside.
An hour in, Solskjær's two-up-top gamble paid off when Cavani timed his run perfectly and dinked a finish past the keeper.
The third goal came when Rashford, on for Ronaldo, timed his run to stay onside and slotted home comfortably.
What we learned:
1. Teams win leagues but players win games
Ronaldo may be over the hill (allegedly) but his class remains. A tense deadlock was broken late in the first half by deftly taken volley. And Cavani followed suit with a delicate finish for the second, to all intents and purposes securing the win.
2. Son rampages
The South Korean striker is fast looking like a superstar outgrowing his club. He may have signed a new contract only recently, but expect offers next summer.
3. Makes no sense
For all the incoherence of Manchester United, Spurs are yet to make sense going forward. Son's performance levels don't drop and Moura is a willing dribbler, Kane is not firing and they are not connecting.
4. Kane is not firing
It might seem hard to believe, but the fans are turning against Harry Kane. It was another slow performance, perhaps illustrated late on when the ball bounced off him from the same spot in which Ronaldo buried his volley.
5. Romero showing positive signs
Despite the goals, the Argentinian defender had a pretty good game, showing signs that maybe he can create a partnership with Dier at the back. Consistency has been lacking this season.
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