Maroune Fellani doubled the lead with a volley at the far post from Ashley Young's cross.
Fellaini was once again on scoring sheet as he scored his second goal with a close-range header from Rashford's free-kick early in the second half.
"It's down to everything he does on the pitch, the qualities he has, the important player he is in some hard games where he just takes the ball and scores two great goals like last time in the league cup (against Burton)".
Manchester United will return to Premier League action after the global break when they take on Liverpool at Anfield on Saturday 14 October.
Crystal Palace manager Roy Hodgson appears dejected during the Premier League match at Old Trafford, Manchester. Hodgson has had another week to work with his players on the training ground but they are coming off the back of a 5-0 defeat Manchester City.
Next up for Man United is the small matter of a trip to Liverpool after the worldwide break, while Palace's search for their first league point of the season will continue away to the champions Chelsea next time out.
He was replaced by 24-year-old debutant Freddie Ladapo, who has scored most of his goals for non-league Grays and Margate, in the second half. I think only a strong character could resist the difficulties here because he had some hard times when people didn't recognise his qualities, when probably other managers didn't like so much the qualities he has. Overall, they lost nine of their last 10 league matches.
Marouane Fellaini went on to add two scores for United.
However, their most recent victory over Manchester United came in the League Cup in November 2011 - Darren Ambrose and Glenn Murray scoring in a 2-1 win in the quarter-final. "And make certain we don't get beaten 4-0 by the next team we play".