Defending champions Lille were left still looking for their first win of the new French season after Saidou Sow’s late equaliser secured a 1-1 draw for Saint-Etienne on Saturday.
Burak Yilmaz, the veteran Turkish striker who was Lille’s top scorer on their remarkable run to the title in May, had earlier given the visitors the lead with a snap-shot late in the first half.
But Saint-Etienne equalised with four minutes remaining when teenage defender Sow met a corner with a towering header, sending the ball over Lille goalkeeper Ivo Grbic – making his debut after signing on loan from Atletico Madrid – and into the net.
Lille, whose title-winning coach Christophe Galtier left for Nice in the close season, have started this Ligue 1 campaign with two draws either side of a 4-0 home hammering by Nice.
Monaco came third last season to earn a crack at the Champions League but their start has been even worse: after taking one point from their first two outings the principality side went down 2-0 at home to Lens on Saturday.
Second-half goals by Cameroonian forward Ignatius Ganago and substitute Simon Banza gave Lens the victory at the Stade Louis II, leaving Monaco eight points behind leaders Paris Saint-Germain already.
For Monaco, much now rests on the second leg of their Champions League play-off tie against Shakhtar Donetsk, with Niko Kovac’s side heading to Ukraine on Wednesday trailing 1-0 after the first leg as they chase a spot in the group stage.
Ganago gave Lens the lead six minutes into the second half, easily getting away from Strahinja Pavlovic to break into the box and score.
The away side then lost midfielder Cheick Doucoure, sent off for a challenge on Krepin Diatta just after the hour, but Monaco could not make their one-man advantage count.
Indeed they had Aleksandr Golovin sent off for a dangerous tackle on Banza late on, and Lens sealed the win in added time as Przemyslaw Frankoswki squared for Banza to finish.
“To maintain the same level of performance as last season, we have to do even more because our opponents now have more of an idea about us,” said Kovac in a damning assessment of his team.
“To be successful again, we will have to fight harder. In football, nothing is taken for granted.”
On Friday, PSG made it three wins out of three as Kylian Mbappe and Angel di Maria both netted in a 4-2 win at Brest.
Ander Herrera and Idrissa Gana Gueye were also on target for a PSG side still missing both Lionel Messi and Neymar, neither of whom is yet fit to play.
French Ligue 1 results on Saturday:
Monaco 0 Lens 2 (Ganago 51, Banza 90+4)
Saint-Etienne 1 (Sow 86) Lille 1 (Yilmaz 38)
Playing Sunday (all times GMT)
Lyon v Clermont (1100), Bordeaux v Angers, Metz v Reims, Montpellier v Lorient, Strasbourg v Troyes (all 1300), Rennes v Nantes (1500), Nice v Marseille (1900)
Brest 2 (Honorat 42, Mounie 85) Paris Saint-Germain 4 (Herrera 23, Mbappe 36, Gueye 73, Di Maria 90)