Dembele completed his protracted switch to the LaLiga giant on Saturday (AEST) for an initial €105 million ($157.7 million), but Dortmund's remaining attacking riches were to the fore at Signal Iduna Park.
Pierre-Emerick Aubameyang made it six for the season in all competitions, earning just reward for early pressure as Peter Bosz's side resumed in the same mood that saw Wolfsburg put the sword 3-0 on the opening weekend.
Christian Pulisic dazzled throughout for the hosts, who extended their advantage in the 57th minute through Nuri Sahin's scorching strike from the edge of the penalty area.
It leaves Dortmund ahead of Bayern Munich and Hamburg on goal difference at the top of the fledgling Bundesliga table heading into the international break.
Aubameyang passed up an early opportunity with an ungainly air shot and barely made better contact in the 15th minute, not that it mattered.
Sahin whipped in an inviting ball from the left and the Bundesliga's leading marksman from last season stole half a yard on Karim Rekik to guide the ball left-footed into the far corner.
Hertha was struggling under wave after wave of Dortmund attacks and Rune Jarstein saved well in the 27th minute when Pulisic cut in from the right to fire towards goal.
After the half hour the visitors enjoyed their first chance of note, when Niklas Stark connected with Marvin Plattenhardt's free-kick from deep, but Roman Burki was up to the task.
Pulisic's burgeoning talent has been a source of comfort for many Dortmund fans throughout the Dembele saga and the 18-year-old United States international continued to go through the gears after half-time.
He collected a pass from Gonzalo Castro in the 52nd minute and drove towards the Hertha defence, whistling a shot past the post, and the winger was unsurprisingly involved when Dortmund doubled its advantage.
Pulisic's cross evaded a pair of Hertha defenders and Maximilian Philipp was unable to turn towards goal, with the ball breaking for Sahin to unleash a venomous shot into the top-right corner.
Mario Gotze was granted a standing ovation when he made way for Shinji Kagawa in the 63rd minute, but Hertha threatened to puncture the party atmosphere soon afterwards when Sebastian Langkamp rose highest on the end of Plattenhardt's corner and Burki clawed to safety.
Vladimir Darida's improvised attempt from Mitchell Weiser's low cross trickled just wide with 20 minutes remaining as Dortmund's concentration seemingly wavered.
But Hertha's challenge faded as an afternoon of defensive toil took its toll and Philipp swiped over when he should have added a third in the 78th minute.
Castro then shot too close to Jarstein at close quarters, while his opposite number Burki concluded an assured outing by denying Mathew Leckie in stoppage-time for back-to-back clean sheets.