Ten-man Monaco suffered a damaging 3-1 defeat to Lyon on Sunday that hands Ligue 1 leaders Nice a real boost in the title race.
Rachid Ghezzal, Mathieu Valbuena and Alexandre Lacazette - who also missed a penalty - scored the goals to end Monaco's seven-game winning run at home in the league and saw Nice stay four points clear after their win over Dijon.
Tiemoue Bakayoko bagged a consolation for the home side at Stade Louis II, who had four players booked and Benjamin Mendy sent off in an ill-tempered match that saw some controversial moments.
Ghezzal fired in the opener just before the half-hour mark and Mendy's kick on Corentin Tolisso earned him a straight red card to give Monaco a real mountain to climb before the break.
Leonardo Jardim's side were furious not to be awarded a penalty shortly after half-time when Valere Germain's effort struck the hand of Lucas Tousart on the line and their frustrations grew when Lacazette won a spot-kick for the visitors following Fabinho's foul.
Danijel Subasic saved the striker's tame effort from 12 yards but their hopes of a comeback were short-lived, with Valbuena steering in Ghezzal's cross on 65 minutes to double Lyon's lead.
Jemerson saw a headed goal ruled out for offside before Bakayoko did give Monaco a lifeline with a deflected drive following some good interplay between Thomas Lemar and Nabil Dirar.
But Lacazette chested down and smashed home after Subasic beat a corner into his path to secure the victory for Lyon and move them to within five points of champions Paris Saint-Germain, who sit third.
