The French giants scored all three goals inside the opening half an hour, with Ibrahimovic's double sandwiched in-between young defender Marquinhos' close-range strike.
From then on, the home side seemed to take their foot off the gas, but it hardly mattered as they followed up their opening 4-1 triumph at Olympiacos with another comprehensive win at the Parc des Princes on Wednesday.
There will be bigger tests to come for PSG, but they proved they will be a force both home and abroad this season as they moved to the top of their group.
They made the ideal start, with Ibrahimovic finishing a flowing move in the fifth minute. Gregory Van Der Wiel ran onto the ball in the right side of the penalty area before sliding to Ibrahimovic at the back post and the Swede tapped into an empty net.
Brazilian defender Luisao should have done better than direct a weak header at PSG goalkeeper Salvatore Sirigu immediately after.
It proved a crucial miss as Laurent Blanc's men doubled their lead after 25 minutes through Marquinhos.
Benfica failed to clear their lines from a corner and some inspired touches helped Blaise Matuidi burst forward to the left touchline.
The French midfielder's cross was deflected into the path of 19-year-old Marquinhos, who could not miss from very close range.
It was the Brazilian 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 Thiago Motta's corner.
It seemed a case of damage limitation for Benfica, who had been badly exposed at the back, with PSG's attackers running rampant.
Their chances were limited to long-distance efforts although Sirigu was nearly at full stretch to keep out Ezequiel Garay's 25-yard curling free-kick just after half-time.
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 Miralem Sulejmani's shot across goal.
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 Lucas Moura's 25-yard drive.
Artur then had to be at his best after tipping away Van Der Wiel's cross into the path of Edinson Cavani, who shot tamely at Benfica's custodian with the goal seemingly at his mercy.