Colombian striker Radamel Falcao scored twice as Monaco thrashed Bastia 5-0 to move top of Ligue 1 on Saturday, while French champions Paris Saint-Germain crashed to a shock 3-0 defeat at Montpellier.
However, the day's action in France was scarred when the game between Metz and Lyon was abandoned after Portuguese goalkeeper Anthony Lopes was hit by a firecracker, prompting fears that the Lyon star may have lost his hearing.
At the Stade Louis II, Kylian Mbappe struck a 10th-minute opener before Monaco dismantled Bastia with four second-half goals in 11 minutes -- Thomas Lemar and Guido Carrillo netting either side of Falcao's brace.
Leonardo Jardim's side rebounded from the disappointment of Tuesday's 1-1 draw at Dijon to provisionally overtake Nice on goal difference, with the erstwhile leaders at home to Toulouse on Sunday.
PSG's five-match winning run in the league was ended in stunning fashion by Montpellier as the 2011-12 champions struck just before half-time through Paul Lasne with Ellyes Skhiri adding a second shortly after the break.
Ryad Boudebouz capped a remarkable afternoon at the Stade de la Mosson with a terrific individual goal 10 minutes from time as Unai Emery's PSG remained a point behind both Monaco and Nice.
"Montpellier were very efficient with the chances they had, while we were not," PSG defender Marquinhos told Canal+ Sport.
"It was a difficult match, Montpellier were good as a unit in defence. After they scored the first goal, it was very difficult.
"We can't commit the same errors in our upcoming games if we want to be champions. We have to get back to work straight away."
PSG face Ludogorets of Bulgaria in the Champions League on Tuesday as they try to seal top spot in Group A before taking on Nice next weekend, but they were blindsided by a Montpellier outfit that had won just three times in 15 matches this season.
The visitors were without midfield trio Marco Verratti, Adrien Rabiot and Thiago Motta as 19-year-old Christopher Nkunku was drafted in by Emery for his first league appearance this term.
The teenager should have put PSG in front from Angel Di Maria's left-wing cross with just six minutes gone, but his close-range header was turned away well by Laurent Pionnier.
Montpellier, whose last win over PSG in the league came in May 2010, grabbed the lead three minutes before the interval as Lasne latched onto a long ball out of defence and lobbed an advancing Alphonse Areola.
Skhiri doubled Montpellier's advantage three minutes into the second half as Morgan Sanson chased down a loose ball before laying it back to edge of the area for the former to curl home superbly.
A mix-up between Vitorino Hilton and Daniel Congre presented Di Maria with a chance to halve the deficit, but the Argentine fired straight at Pionnier on 53 minutes.
The Montpellier keeper then blocked with his legs to deny Lucas with Blaise Matuidi subsequently blazing over from Layvin Kurzawa's cutback.
Algeria international Boudebouz extinguished any prospect of a late PSG revival as he ran from inside his own half before arrowing a low strike beyond Areola for Montpellier's third.
Lyon's match at Metz was abandoned after just half an hour at the Stade Saint-Symphorien as visiting goalkeeper Lopes was targeted by firecrackers thrown by home supporters.
Metz had taken the lead through Gauthier Hein shortly before play was interrupted at the Stade, with the match officially called off after a 45-minute delay.
Lyon said Lopes, left dazed by the incidents, was on his way to hospital to undergo tests as images showed a projectile exploding underneath the prone Portugal international.
"At worst the eardrum could be affected," Lyon president Jean-Michel Aulas told BeIN Sports.
"He has a loss of balance and he doesn't know where he is. That's why he was taken to the hospital. The team will wait for him and hope it's nothing serious."
Guingamp climbed into fourth after a 2-0 win over second-bottom Nantes, who are without a manager after the dismissal of Rene Girard this week.