First-half goals from Alejandro Garnacho and Casemiro set United on their way to a place in the last 16, with the Brazilian providing the cross for Anthony Martial’s clinical first-time effort 10 minutes after the restart.
Having faced various forms of chaos in the past few weeks, this was the kind of straightforward night United manager Erik ten Hag must have longed for as his side completed the biggest win of a season in which they have struggled so far.
With Mason Mount back in the starting XI and fellow summer signing Sofyan Amrabat making his first start – albeit at left-back – Ten Hag was at least able to integrate to an extent some key pieces of his United puzzle.
Plenty of instances of controlled possession, which many supporters have been disappointed Ten Hag has failed to implement so far, were on display too.
Evidently, the gameplan was to create an overload on the United right with lofted cross-field passes from the left, which both Amrabat and Mount were able to execute.
Morocco international Amrabat in particular caught the eye as an inverted left-back. The on-loan Fiorentina man’s early shot was poor, but he was excellent aside from that and demonstrated an excellent passing range, plenty of energy and an ability to spot danger when it arose.
Fellow full-back Diogo Dalot created the opener when he burst onto Facundo Pellistri’s pass and pulled a low cross back for Garnacho to finish, before Mount’s superb corner picked out Casemiro six minutes later to double the hosts’ lead and effectively end the contest.
Martial’s strike from an acute angle was his first goal of the season and came in his first appearance at Old Trafford since Ten Hag was booed for bringing him on in place of Rasmus Hojlund against Brighton.
Having been a spectator for most of the night, goalkeeper Andre Onana was called upon to make two excellent late saves, denying two close-range efforts from Palace striker Jean-Phillippe Mateta on both occasions.
To cap a disappointing night for the Eagles, who return here in the Premier League on Saturday, goalkeeper Dean Henderson only lasted 19 minutes on his debut against his former club as he was forced off with muscular pain after making a routine clearance.