Crawley handed plum draw at Old Trafford
Another draw that captured fully the romance of the competition pitted League One Leyton Orient against London rivals Arsenal at Brisbane Road.
"I'm confident we'll get the whole town up there. There will be a procession of buses going," Crawley chief executive Alan Williams told Sky Sports from a packed function room at the southern England club.
Crawley went through to the last 16 with a 1-0 victory at League Two Torquay United on Saturday, their third Football League scalp in successive games.
"We never had any money forecast (in our budget) for the FA Cup this year because we keep losing in it," a beaming Williams added. "We hadn't won a cup game for eight years."
Manager Steve Evans said: "If there's any non-league club capable of beating Manchester United it's Crawley Town".
Orient chairman Barry Hearn was also delighted with his club's draw.
"The tie of the round is without a doubt Leyton Orient against Arsenal," joked Hearn. "This is our biggest game for 30 years."
Holders Chelsea, if they beat Everton in a replay, will host Championship club Reading in the fifth round while Manchester City will entertain Aston Villa providing they defeat League One Notts County in a replay.
The fifth round will take place on the weekend of February 19 and 20.