Champions PSG were rarely troubled in their win at the Stade de la Route de Lorient and made it back-to-back successes in France's top flight.
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Thiago Motta opened the scoring on 19 minutes with a superb curing effort that found the corner, as Laurent Blanc's men led 1-0 at half-time.
The visitors were awarded a penalty shortly after the restart when Blaise Matuidi was felled in the area by Cedric Hountondji. Sweden star Zlatan Ibrahimovic duly converted from 12 yards, taking his Ligue 1 tally to 14 for the campaign.
Rennes winger Romain Alessandrini reduced the deficit on 67 minutes to ensure a nervy ending for PSG, but Edinson Cavani wrapped up the three points for the visitors in injury time.
However, Monaco ensured the gap at the top of the table remained at two points with a comfortable 2-0 triumph at 10-man Guingamp.
Forward Anthony Martial put Claudio Ranieri's men ahead on four minutes, and the visitors' situation improved further as full-back Jonathan Martins Pereira was shown a second yellow card.
The match was then sewn up three minutes before half-time through an unlikely source in left-back Layvin Kurzawa.
Meanwhile, Nantes harbour ambitions of finishing in the top three and among the UEFA Champions League positions, but their hopes were dealt a blow in a 2-1 home defeat against Toulouse.
After a goalless first-half at the Stade de la Beaujoire, the visitors stole into a two-goal lead thanks to strikes from Etienne Didot and Jean-Daniel Akpa Akpro.
Papy Djilobodji halved the deficit in the 82nd minute, but Michel Der Zakarian's charges failed to find a leveller.
At the other end of the table, Sochaux's woes continued in a 1-0 defeat at Nice, who ended a seven-match losing streak in the process.
For Sochaux the result represented their 12th defeat from 18 top-flight matches this term, and leaves them rooted to the bottom of the table with just eight points.
Fellow strugglers Ajaccio fell to a 2-1 defeat at home to Lorient, as Jeremie Aliadiere's strike made it five straight league victories for Christian Gourcuff's men.
Elsewhere, Floyd Ayite's injury-time leveller secured Reims a 1-1 draw at Evian.