Romain Alessandrini pulled a goal back for the Breton hosts midway through the second half but Edinson Cavani's injury-time low strike sealed the points.
The victory kept PSG two points clear of second-placed Monaco, who won 2-0 at Guingamp later on Saturday.
But with just 11 points dropped in 18 matches this season, PSG appear well on their way to maintaining their grip on the Ligue 1 crown.
If there was any doubt about the Parisians' current morale after two defeats in their last three matches, they were dispelled in a controlled performance.
PSG's 2-0 loss at Evian two weeks ago ended a 36-match unbeaten run but their midweek reverse at Benfica in the UEFA Champions League came with several stars rested and after the French champions had already secured top spot in their group.
In between those two setbacks they had thumped lowly Sochaux 5-0.
"We lost two away matches because I think we lacked the ingredients needed for such high-level matches," PSG coach Laurent Blanc said.
"Tonight, apart from the victory, the overall performance really pleased me. The players rediscovered their spirit."
It was a game punctuated by some fine goals, most of all the opening one.
Motta was fully 25 yards out when he shifted the ball onto his favoured left foot and hit a powerful effort that curled around goalkeeper Benoit Costil.
The second came as Blaise Matuidi made a surging run into the box following a one-two, only to be sent crashing to the ground by a sliding challenge from Cedric Houtondji.
Ibrahimovic calmly rolled the spot-kick home straight down the middle for his 14th goal of the season, keeping him top of the scoring charts.
Rennes' hopes were revived when Alessandrini cracked home a free-kick from as far out as Motta's goal, but PSG goalkeeper Salvatore Sirigu should have done better with a strike that seemed to go straight through him.
The final nail in the home coffin came in time added on as Cavani robbed the ball in his own half and sprinted up the field to take Matuidi's pass from a swift counter before shooting home from outside the area.
Monaco make it five in a row, Nantes slip
Monaco, without injured record signing Radamel Falcao for the fourth game in a row, won for the fifth successive match.
It was all but over at half-time as Anthony Martial shot high into the net from James Rodriguez's pass after just four minutes.
And three minutes from time a Rodriguez corner was headed home by Layvin Kurzawa.
In other games, Nice, who narrowly missed out on qualifying for the Champions League last season, finally ended a seven-match losing streak with a 1-0 success at home to rock bottom Sochaux.
Nantes' hopes of closing in on the Champions League places suffered a blow with a 2-1 defeat at home to Toulouse, which leaves them seven points off third-placed Lille, who have a game in hand.
On Friday, 2012 champions Montpellier's dismal season continued as a 1-0 defeat at home to Saint-Etienne left them still one place above the relegation zone.
Montpellier have not won in nine matches since early October and have only two wins all season.
They fired coach Jean Fernandez in early December, replacing him with Rolland Courbis.