Saint-Etienne ended Monaco's four-game winning streak with a decisive 3-0 home win on Sunday.
Fifth-placed Monaco, unbeaten in Ligue 1 since Dec. 16, had no answer to the pressure from Saint Etienne, who had not won at home in the championship since October.
Goals by Blaise Matuidi in the 13th minute, Argentine striker Gonzalo Ruben Bergessio a quarter of an hour from the end and Emmanuel Riviere just before the finish lifted St Etienne to 16th place in the table.
Fourth-placed Olympique Lyon, down to 10 men after Jean Makoun was sent off in the 68th minute for a second yellow card, saved a point with a 0-0 draw at Toulouse.
Olympique Marseille thrashed Valenciennes 5-1 in Sunday's late game to move into fifth spot. Goals from Lucho González, Brandao, Benoit Cheyrou, Mathieu Valbuena and Mamadou Niang sealed the rout. Carlos Sanchez got a consolation for the visitors.
At the end of the 23rd round, Girondins Bordeaux still head the table on 48 points after their 3-0 loss to Stade Rennes on Saturday, ahead of Montpellier who cut the gap at the head of the table with their 2-0 victory over Boulogne-sur-Mer.
