Mohamed Fofana seized his chance to give Reims a little breathing space in their battle to avoid the drop from Ligue 1.
The Malian defender headed the only goal in the 31st minute against Rennes to make it a miserable 500th top-flight match as a manager for visiting boss Frederic Antonetti.
Antonetti is the longest serving of the current crop of Ligue 1 managers but this was not a night to remember for Rennes. Their hopes of playing in Europe next season are fading after five games without a win.
Reims, who were outside the relegation zone at the beginning of the day, moved two points clear.
Rennes had the first chance when Kevin Theophile Catherine was played in by Romain Danze and took on Nicolas de Preville before his lob was well read by goalkeeper Kossi Agassa.
Reims went ahead when Antoine Devaux was allowed too much space on the left and centred for Fofana at the far post to head back across goal and into the net, with goalkeeper Benoit Costil well beaten.
Brazilian midfielder Diego threatened to snatch a second goal for Reims just before half-time, but sent his shot wide after taking on a pass from Nicolas Fauvergue.
Rennes had the clear chances in the second half.
From the first, Jean Makoun released Jonathan Pitroipa in the left side of the penalty area and a curled right-footed shot went narrowly over the crossbar.
Theophile Catherine created the next opening when his cross reached Alou Diarra via both Danze and Cheick Fantamady Diarra. The France international took aim from the edge of the penalty area and cracked his shot against the right post.
Soon the chances would dry up, but not before Danze made progress down the right and crossed to Makoun who from inside the six-yard box headed inches wide.