Crawley breezed into the FA Cup third round at the expense of Chelmsford.
Red midfielder Nicky Adams opened the scoring when his cross-shot crept in at the near post.
Blue Square Bet South side Chelmsford were reduced to 10 men when Donovan Simmonds picked up his second yellow, and Billy Clarke's volley made it 2-0 before half-time.
Gary Alexander's late penalty - awarded after Anthony Cook brought down Sergio Torres - put the result beyond doubt.
The visitors had keeper Stuart Searle to thank for keeping the score down, the former Crawley man saving well from Hope Akpan and Alexander in the second half.
VIEW FROM THE DRESSING ROOM
Crawley Town boss Richie Barker told BBC Sussex:
"I thought the players attitude was fantastic right from the first minute, they were excellent.
"The extra money in the next round would be great. Helping the football club with a big draw would make a difference to us.
"Over the last few years this club have had some decent ties, but we won't be getting too carried away yet."