After missing a penalty, Adrian Ramos scored twice while Sami Allagui was also on target as the visitors to the HSV-Arena completed the job within the first 45 minutes.
Hamburg, who have the worst defensive record in the division, have now lost six games in a row and are two points adrift of safety, second from the foot of the Bundesliga.
Despite receiving assurances that his job would be safe even in the event of a defeat, Hamburg coach Bert van Marwijk's future is nevertheless uncertain with few expecting them to capitulate so convincingly at home.
Hertha quickly imposed themselves on the game, taking advantage of Hamburg's clear insecurities and amplifying them.
After going close with two free-kicks, they won a penalty when Hajime Hosogai was felled by Heiko Westermann inside the penalty area.
Ramos stepped up but Rene Adler, back in the Hamburg goal after a long injury absence, guesed the right way and pushed the ball behind for a corner.
The danger was averted only temporarily, though, as Allagui put the ball in from the corner after Ramos flicked the ball on to him at the far post.
Ramos was always in the thick of the action and he made up for his penalty miss by heading Hertha two up in the 23rd minute, beating Johan Djourou in the air from close range.
Things then went from bad to worse for Hamburg as Ramos exchanged passes with Johannes van den Bergh to be presented with only Adler to beat, and he held his nerve this time to join Borussia Dortmund's Robert Lewandowski at the top of the scoring charts on 14.
Hamburg left the field to a chorus of disapproval from the suffering home fans, who did not help them in the second half either, quick to jeer every misplaced pass.
Indeed, the hosts, rather than looking for a route back into the game, appeared more intent on limiting the damage in the second 45 minutes.
They almost failed to do even that as Hertha substitute Ronny went close to making it four in the final five minutes of what was already a game to forget for Hamburg, the lowest ebb in their season so far.