Although Wes Brown's 28th minute header ended their dream of becoming the first non-League side for 97 years to reach the last eight, Crawley left behind a performance that would not have disgraced teams much higher up the ladder.
Crawley, whose main claim to fame is being the nearest town to Gatwick Airport, almost equalised in stoppage time at the end of the match when Richard Brodie's looping header hit the top of United goalkeeper Anders Lindegaard's crossbar.
A goal then would have been just reward for the way the non-League outfit from Sussex battled against the Premier League leaders and 11-times record FA Cup winners in front of almost 75,000 fans at United's 'Theatre of Dreams'.
"It didn't matter what the scoreline was today, it was their day - there's no question about that," United manager Sir Alex Ferguson told MUTV. "They deserved a draw, really, on the second half, with the effort they put in, the commitment.
"Sometimes you get the breaks in the cup and you struggle through one round. We've done that in the past and it was another example today."
Forward Sergio Torres typified Crawley's approach with a hard-running game and left with a clump of Old Trafford grass in his sock as a memento of the night.
They also dominated for a long spell in the second half and maintained pressure on United's goal with the post-match statistics revealing they enjoyed 53 percent of possession.
A measure of Crawley's resistance was that Ferguson, who described them before kickoff as "the best non-League side for quite a while", brought on Wayne Rooney at halftime.
"They made it very difficult for us and we were second to every ball," said Ferguson. "It's disappointing. But we had some players who maybe don't understand what FA Cup football is like. Maybe for them it's the biggest lesson."
Crawley captain Pablo Mills, named Man of the Match, told ITV: "I thought we could have made their keeper work a bit more.
"The lads put a great shif
