Paris Saint-Germain suffered a shock setback in their pursuit of Nice with a 3-0 defeat in Montpellier, their heaviest loss in Ligue 1 since November 2011.
Goals either side of the interval from Paul Lasne and Ellyes Skhiri respectively, followed by a late Ryad Boudebouz strike, proved more than enough to hand Unai Emery's team their first defeat in nine league outings.
Defeat for the current champions, their first in Montpellier in the league since 2004, leaves them adrift of top spot by a single point with Nice still to host Toulouse on Sunday evening.
Monaco took advantage of PSG's stumble to claim top spot overnight with a comprehensive 5-0 victory over struggling Bastia at Stade Louis II.
Leonardo Jardim's side knew a win would be enough to send them to the summit on goal difference over Nice.
Kylian Mbappe got the hosts on their way with the opener on 10 minutes and they fired in four second-half goals to extend their unbeaten league run to seven games.
Radamel Falcao bagged a brace while Thomas Lemar and Guido Carrillo condemned Bastia to a ninth Ligue 1 game without a win.
Lyon were hoping to add to their impressive run of four wins from their last five games but the clash at Metz was abandoned after firecrackers were thrown onto the pitch.
Gauthier Hein's goal for Metz on 28 minutes was followed shortly after by a number of explosives being thrown from fans, including one which landed next to the head of Lyon goalkeeper Anthony Lopes before going off.
Elsewhere, Nicolas de Preville's solitary goal clinched Lille a 1-0 victory at Bordeaux and their first win on the road in Ligue 1 this season.
Lorient remain rooted to the foot of the table after a 2-2 draw away at Angers.
Lorient took the lead through Sylvain Marveaux on 23 minutes but moments later they were pegged back by Famara Diedhiou's penalty.
Cheikh N'Doye put the hosts in front on 58 minutes before Abdul Majeed Waris levelled for Lorient, who are now unbeaten in three games.
Nantes, who earlier this week parted company with coach Rene Girard, remain second from bottom after Guingamp gained their first league win in five games with a 2-0 triumph at Stade du Roudourou.
Jimmy Briand put the hosts ahead in the 22nd minute after an assist from fellow attacker Yannis Salibur, who on 63 minutes doubled the lead having received the ball from Brazilian defender Fernando Marcal.