Rashford's late goal earned United a 2-1 victory away to Paris Saint-Germain last week and at Old Trafford the England striker came on as a second-half substitute and scored three times
The home side were put under pressure by Julian Nagelsmann's team but substitute Rashford struck three times after coming on in the 63rd minute to put the result beyond doubt.
Just when it looked like United's 6-1 collapse at home to Tottenham would be the day's biggest shock in the Premier League, Liverpool managed to surpass it with 7-2 defeat to Aston Villa
For Tottenham, Harry Kane and Son Heung-min scored two goals each. To make the matters worse, United also lost Anthony Martial in the first half as he was given a red card for an altercation with Tottenham's Erik Lamela.