The win sent Thomas Tuchel’s men five points clear of Lille who play at Brest on Sunday.
Moise Kean opened for the hosts after 11 minutes. The 20-year-old Italy international picked up a deflected clearance off Angel Di Maria just outside the penalty area and swept the ball past the Rennes goalkeeper Alfred Gomis.
The strike came against the run of play. But the second - midway through the half - came after sustained pressure from the reigning Ligue 1 champions.
Di Maria scurried on to Ander Herrer’s defence splitting pass and dinked over a sprawling Gomis.
Misses
Steven Nzonzi could have halved the deficit immediately but he put his header wide from Benjamin Bourigeaud’s free kick.
His miss encapsulated Rennes' plight - chunky phases of possession but a lack of cutting edge.
Di Maria showed how to be clinical after 66 minutes. The ball broke loose to the right of the area and he slapped a left-fooedt shot into the bottom left hand corner.
It was so quick and instinctive it silenced the Rennes defenders and highlighted the gulf between the teams.
