Nice capitalised on Monaco's slip-up to move four points clear at the summit of Ligue 1 courtesy of a 2-0 win over 10-man Lyon, despite Mario Balotelli having a penalty saved.
With Leonardo Jardim's men falling to a 3-1 loss at Toulouse – conquerors of champions Paris-Saint Germain in their previous home match – captain Paul Baysse's early strike and Jean Seri's second-half effort ensured Nice took full advantage.
Nabil Fekir's dismissal only made the visitors' task more difficult at the Allianz Riviera and they remain without a top-flight win on the road since their opening game.
The hosts, boosted by Balotelli's presence after his red card versus Lorient was rescinded, led with only five minutes gone as Malang Sarr nodded a looping delivery into the path of Baysse to rifle past Anthony Lopes.
Fekir was given his marching orders when he tripped and then trod on the goalscorer just before the half-hour mark.
Balotelli caused a brief panic among the home fans when he went down clutching his head following a mid-air collision with Jeremy Morel in the second half, but the Italian soon picked himself up.
Seri added the second 14 minutes from time, striking a bobbling shot into the left-hand corner after Younes Belhanda had been denied by the post.
Balotelli should have added late gloss and a sixth Ligue 1 goal of the season, but, having been fouled in the box by Jordy Gaspar, his stuttering run-up preceded a tame effort that was kept out by Lopes.
Monaco's defeat was inflicted by Martin Braithwaite's hat-trick after former Nice loanee Valere Germain had given them the lead.
