Soon after the re-start, United killed the game off with Fellaini scoring again, via a header, this time from a Rashford free-kick.
Palace have scored just four goals in their previous 12 top-flight matches, a date spanning back until April, with all of them coming in a 4-0 win over now-Championship side Hull City.
José Mourinho is frustrated that Manchester United's momentum will be halted by the October worldwide break. The visitors saw much more possession than they had in the first half, but nudged it around with neither urgency nor inspiration. Rashford had two assists in a single game for the first time in his United career during the victory.
Last-place Palace has conceded nine goals in two trips to Manchester in the space of a week, having lost 5-0 at City last weekend. I need some people with maturity, I need some people with the concept of team, I know that the new generations are more individual because this is the way the entourage and society makes them.
United's terrific 4-1 win over CSKA Moscow in Russian Federation gave Mourinho's men a three-point lead in their group. In 2007-08, for example, Derby won one game and finished with 11 points after making the jump (though even they scored 20 goals).
Taking Gabriel Jesus's pass in stride, De Bruyne advanced unchecked to the edge of the penalty area and smashed a fierce strike past Courtois for his first league goal this season.
Palace's campaign started miserably under Frank de Boer and has not yet improved under the former England manager, with the south Londoners entering the October global break rock bottom of the standings.
The veteran striker has been without a club since leaving Pescara after just three games and no goals last season.
"He is an experienced coach with good players".