In his ninth league appearance, Ibrahimovic toyed with four defenders before nonchalantly firing a shot just past Guy Roland Ndy Assembe 15 minutes from time to put PSG on 22 points.
Carlo Ancelotti's side lead second-placed Toulouse, who beat Stade Brest 3-1, by three points before third-placed Marseille, also on 19 points, take on fourth-placed Lyon on Sunday.
Nancy remain last on five points.
Once again PSG had Ibrahimovic to thank as they suffered against a bold Nancy side, who came close in the first half when Benjamin Moukandjo's 18-metre strike smashed against Salvatore Sirigu's left post.
Ancelotti's side also had their chances before the break through Mamadou Sakho and Kevin Gameiro but the two were denied by brilliant saves from Ndy Assembe.
Ibrahimovic dipped a shot from 35 metres just over the bar in the 70th minute as PSG increased the pressure.
While Jeremy Menez wasted a couple of great opportunities, Ibrahimovic made the most of the little space he had with 15 minutes left to score the only goal.
Wissam Ben Yedder scored his seventh goal of the season to help Toulouse sweep past Stade Brest.
Champions Montpellier moved up to 12th on 11 points thanks to a 3-1 home victory against Nice.
Lille ended Valenciennes's brilliant run with a 2-1 home win against their neighbours who were reduced to 10 men.
Valenciennes, who had scored 12 goals in their last three league matches, lacked inspiration and fell behind in the second minute when Gaetan Bong deflected a Nolan Roux shot into his own goal.
Dimitri Payet made it 2-0 four minutes before the interval after Carlos Sanchez had been sent off for a second booking in the 28th. Anthony Le Tallec scored a consolation goal in the second half.
The game between Sochaux and Evian Thonon Gaillard was called off because of snow.
On Sunday, Bordeaux will look to stretch their unbeaten series to 10 league games when they travel to Bastia.