Having seen their UEFA Champions League dreams effectively dashed by a 3-1 quarter-final first-leg defeat to Barcelona in midweek, PSG turned their attentions back to an enthralling battle for the domestic title with seven-time champions Lyon on Saturday.
And, despite the absence of Ibrahimovic - banned for three games for a foul-mouthed rant following last month's 3-2 loss at Bordeaux - and injured captain Thiago Silva, PSG did enough to see off a determined Nice side at the Allianz Riviera.
The defending champions took the lead thanks to an assured 39th-minute finish from Pastore, only for former PSG man Mathieu Bodmer to equalise just before the interval.
Laurent Blanc's men found another gear in the second half, though, and Pastore duly restored PSG's advantage with a powerful finish into the bottom-right corner.
A 69th-minute penalty from Edinson Cavani made sure of the points after the Uruguay striker had been fouled by Jordan Amavi, securing a victory that sends PSG a point clear of Lyon - who host Saint-Etienne on Sunday.
Nice started brightly and went close to opening the scoring in the 15th minute when Algerian forward Said Benrahma curled narrowly wide of the left-hand post.
PSG, also without the presence of the banned Marco Verratti, struggled to get into any sort of rhythm in the opening 45 minutes, which Nice largely controlled without creating much in the way of goalscoring opportunities.
The hosts' failure to take advantage of their period of superiority was punished by Pastore six minutes before the break.
The Argentina international latched on to Lucas Moura's pass and coolly slotted the ball beyond Simon Pouplin.
But Nice responded well and equalised on the stroke of half-time, as Bodmer flicked home Benrahma's low drive after PSG had only half cleared a left-wing free-kick.
Pouplin was forced to show brilliant reactions to preserve parity three minutes minutes after the interval, the goalkeeper turning David Luiz's close-range strike over the crossbar following Nice's failure to deal with a corner.
Salvatore Sirigu then demonstrated his reflexes at the other end, as the Italy international dived to his left to tip Carlos Eduardo's header against the right-hand post.
Yet it was Pouplin whose goal came under more sustained pressure in the second half. The former Rennes man did well to cut out Lucas Digne's cross-cum-shot before seeing Luiz clatter the underside of the crossbar with a header.
Pouplin's goal was finally breached for a second time in the 63rd minute, though, Pastore lashing a shot in on the rebound after his initial volley had been blocked by the Nice shot-stopper.
Just six minutes later, the game was put beyond Nice as Amavi tripped Cavani in the box, allowing the former Napoli man to emphatically fire home from 12 yards.
