Fourth-placed Paris Saint-Germain slipped five points behind after a 1-0 loss at fifth-bottom Auxerre, who boosted their survival hopes with Kamel Chafni's 86th-minute strike from outside the area.
Referees from the third division were brought in to officiate the day's top-flight games after a row between the French football federation and the usual referees, who had wanted to delay the kick-offs in protest at recent criticism.
The officials had little to do in the first halves on Saturday with Rennes the only team to score before the break in seven matches when Razak Boukari expertly volleyed in from just outside the area after 27 minutes at sixth-placed Montpellier.
Montpellier pushed hard for an equaliser but some last-ditch defending and the bar secured the win for Brittany side Rennes.
"It wasn't the prettiest match of the season but we are very happy to take the three points," Boukari told reporters.
Mid-table Sochaux and Caen were the only other sides to score with 1-0 wins over fast-fading duo Toulouse and Saint-Etienne.
With just 12 games left, Monaco's plight continues after the 2004 European Cup runners-up were involved in one of three 0-0 draws at Valenciennes to stay third-bottom and in the drop zone.
