Paris Saint-Germain suffered their second Ligue 1 defeat of the season as Lyon bounced back from their midweek Europa League elimination to edge a 1-0 victory over the leaders to keep the pressure on fourth-placed St Etienne.
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 Stade de 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.
The two sides will meet again in seven days' time in the final of the French Coupe de la Ligue, when Lyon will hope to guarantee a return to the Europa League as well as the season's first silverware.
St Etienne overturned a two-goal deficit to keep their European ambitions on track with a last-gasp 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 saw them finish the weekend still in fourth spot in Ligue 1.
But Lyon are now within two points of what at present is the only league berth which gains entry to the Europa League.
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 of their lowly opponents and gave Michel Der Zakarian's mid-table side only their second win in 13 games.
Defeat for Guingamp left them perilously close to the drop zone, with just five points separating them from third-bottom Evian. Nantes can now start planning for next season after reaching the 40-point mark.