The French giant scored all three goals inside the opening half-an-hour with Ibrahimovic's double sandwiched in-between young defender Marquinhos's close-range strike.
From then on, the home side seemed to take its foot off the gas, but it hardly mattered as it followed up its opening 4-1 triumph at Olympiacos with another comprehensive win at the Parc des Princes.
There will be bigger tests to come for PSG, but it proved it will be a force both home and abroad this season as it moved to the top of the group.
It made the ideal start, with Ibrahimovic finishing a flowing move in the fifth minute.
Defender Luisao should have done better than direct a weak header at PSG goalkeeper
It proved a crucial miss as
Benfica failed to clear its lines from a corner and some inspired touches helped Blaise Matuidi burst forward to the left touchline.
The midfielder's cross was deflected into the path of 19-year-old Marquinhos, who could not miss from very close range.
It was the defender's third goal in five games for PSG, having not managed one goal in 30 appearances for previous club Roma.
The game was all but over as a contest five minutes later when Ibrahimovic rose highest to head into the top corner from
It seemed a case of damage limitation for Benfica, which had been badly exposed at the back, with PSG's attackers running rampant.
Its chances were limited to long-distance efforts although Sirigu was nearly at full stretch to keep out
It was not so much one-way traffic in the second half although there was a definite feeling PSG had taken the foot off the gas.
Sirigu remained impenetrable in the home goal, though, denying 66th-minute substitute
At the other end, Ibrahimovic should have had his hat-trick but could only strike over the bar on the follow-up after Benfica goalkeeper Artur had only managed to parry the influential
Artur then had to be at his best after tipping away