Paris Saint-Germain suffered their second Ligue 1 defeat of the season as Lyon claimed a 1-0 victory over the leaders on Sunday.
PSG, who were knocked out of the Champions League by Chelsea on Tuesday, were hoping to return to winning ways but were beaten after Jordan Ferri handed Lyon the lead just after the half-hour mark at the Stade Gerland.
Laurent Blanc's leaders - last defeated in the league back in December - could have tied up the title with a win had Monaco not beaten Rennes on Saturday, but the two results went against them and saw their lead cut to 10 points with five matches remaining.
St Etienne overturned a two-goal deficit to keep their European ambitions on track with a 2-2 draw at Reims.
Gaetan Charbonnier and Franck Signorino put the home side in control, but Brandao quickly halved the deficit before a stoppage-time strike from Francois Clerc snatched a result which stretched their unbeaten run to four matches and sees them finish the weekend still in fourth spot in Ligue 1.
Nantes' faltering season was given a timely boost with a 1-0 win over struggling Guingamp at La Beaujoire.
Serge Gakpe's early opener - his fourth goal of the season - was all the hosts needed to see off their lowly opponents and gave Michel Der Zakarian's mid-table side only their second win in 13 games.