A Yado Mambo own goal late in the first half followed up by a route one goal scored by Jake Robinson early in the second half gave City a mountain to climb.
Danny Mills’ third appeared to make the points safe before Mambo scored at the right end to reduce the deficit.
But less than a minute later the home side restored their lead after Gerardo Blaco was found unmarked in the area to head home, before Mills was found at the far post from a corner to make it five and rub salt in the wound.
It was therefore a case of third time lucky for Whitehawk who had drawn and then lost to City in the FA Cup in October and manager Mark Hawkes made five changes to the side that drew with Hayes & Yeading last weekend, including a surprise recall for Luke Callander from his loan-spell at Witham.
The midfield also saw academy graduate Harry Morgan make his full debut for the club as he replaced the suspended Mark Hughes, with Yado Mambo taking the captains armband and being joined at centre-half with the returning Mark Haines.
Whitehawk’s captain, Lee Hills, failed to last more than quarter of an hour as he was replaced after 11 minutes by Pa Saikou Kujabi due to injury and the game began much more conservatively compared to the FA Cup meeting between the two last month which had ended 4-4.
Both sides resorted to taking efforts from range as neither goalkeeper was tested early on. Gerardo Blanco’s effort was blocked by Morgan with John-Paul Kissock sending one over after the ball deflected to him on the edge of the area.
And Christian Smith forced Craig Ross into action when his free-kick went through the wall, but straight down the throat of the Whitehawk ‘keeper.
Rohdell Gordon showed some trickery to find space for a cross on the left, evading the goalkeeper but not David Ijaha at the far post with Callander lurking and Callander went close with a free kick that took a slight deflection.
Eventually though the deadlock was broken but in unfortunate circumstances for the Clarets as captain for the day, Mambo, put into his own net to give the home side the lead.
An attack down the right resulted in a low cross coming in towards Danny Mills at the near post. The initial cross was blocked by Rob Girdlestone, but in trying to clear the ball away the ball ricocheted in off Mambo into the bottom corner to put Whitehawk in front.
Mambo and the rest of the Clarets looked like they’d been rocked by the goal and the Chelmsford centre-half almost scored again for the home side moments later after another low cross from the right was sliced just past the far post.
But having made it into the break just one goal down City found themselves two behind early in the second half via route one.
A long punt from the back floated over the high City back line and perfectly into the path of Jake Robinson. The striker composed himself to find the back of the net and double the home side’s lead.
The home side were starting to enjoy their football and were looking threatening each and every time they went forward, and having been the better side by far in the second half they killed the game off when Kissock's low driving cross found Danny Mills to tap home.
With City looking dead and buried Mambo gave City brief hope of staging a come-back as he flicked the ball on from a free kick which was whipped in by Nicky Nicolau, finding the bottom corner.
But any hope of a remarkable come back was short lived as a minute later Whitehawk restored their three goal lead when Robinson crossed, again from the right, to find Blanco unmarked to make it an afternoon to forget for the Clarets.
And with less than 10 minutes remaining Whitehawk rubbed even more salt into the gaping wound as a corner from the right found Mills unmarked at the far post, allowing him to smash the ball in from close range to make it five.
"I'm disappointed. I knew it would be hard today but we've made too many errors and shipped five goals" said boss Mark Hawkes.
"Three, maybe four (of those goals) are down to us, but it's one defeat in nine league games, that's what people have got to remember.
"Days like this in football are going to happen. We had a big part of our midfield missing today...but we're a young team and days like that will happen with young players."
1. Craig Ross
2. Nick Arnold
3. Lee Hills (C)
4. David Ijaha
5. Osei Sankofa
6. Tom Cadmore
7. Gerardo Blanco
8. Sergio Torres
9. Jake Robinson
10. Danny Mills
11. John-Paul Kissock
12. Sam Gargan (On for Danny Mills 85’)
14. Pa Saikou Kujabi (On for Lee Hills 11’)
15. Silvestre Guyonnet (On for Sergio Torres 85’)
16. Sergio Makofo
17. Sam Deering
1. Tony Thompson
2. Rob Girdlestone
3. Leon Redwood
4. Harry Morgan
5. Mark Haines
6. Yado Mambo (C)
7. Evans Kouassi
8. Joe Ward
9. Rohdell Gordon
10. Luke Callander
11. Christian Smith
12. Michael Cheek (On for Evans Kouassi 54’)
14. Nicky Nicolau (On for Harry Morgan 67’)
15. James Love
16. Jason Williams (On for Luke Callander 67’)
17. Marvin Ekpiteta
Referee: Ian Fissenden
Assistants: Alex Gray & Paul Lister
Whitehawk: Yado Mambo O.G. 38’, Jake Robinson 51’, Danny Mills 73’, 82’, Gerardo Blaco 76’
Chelmsford City: Yado Mambo 75’
Whitehawk: Osei Sankofa (Deliberate Handball - 22’), David Ijaha (Professional Foul - 36’), Tom Cadmore (Professional Foul - 36’)
Chelmsford City: Mark Haines (Dissent - 45’), Harry Morgan (Professional Foul – 61’)
City Man of the Match: Christian Smith