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'.
About nine thousand of those supporters were from Crawley, whose average home attendance is 1,800 but who won themselves a lot more admirers with their battling performance.
"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 gained in confidence after being overawed at the start and could have equalised when David Hunt volleyed wide after 72 minutes when the ball fell on his less accurate left foot.
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.
RARE CHANCE
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.
Ferguson, who went to watch Crawley play in midweek, made nine changes from the side that beat Manchester City in the Premier League at Old Trafford last week.
But many of the players given a rare chance to start fluffed their lines and were outrun and outfought by the visitors who could well gain promotion from the Conference to League Two of the Football League at the end of the season.
"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."
Rooney, and his illustrious team-mates, were all outshone for once, with the England striker having little impact against a rugged back line of defenders. Apart from a shot just before the end, he never looked like scoring.
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
