United were expected to steamroll over an opposition that plays in the Blue Square Bet Premier division of the Football Conference, but just eked through via a solitary goal from Wes Brown to advance to the last-eight of the FA Cup.
The goalkeeper, who joined United from Norwegian club Aalesund, told MUTV: "Crawley did a great job.
"It's a cup match and I've heard from the manager in the last few days that in the FA Cup anything can happen. This match was evidence of that. With a bit more luck, Crawley could have scored.