Leonardo Jardim's side salvaged a point when Bernardo Silva scored after the interval to cancel out Sadio Diallo's first-half opener for Bastia.
Monaco, who travel to City for a Champions League last-16 first-leg game on Tuesday, have 59 points from 26 games, four ahead of second-placed Paris St Germain before the champions host Toulouse on Sunday.
With Fabinho and Kylian Mbappe on the bench, Monaco struggled to play the football that helped them score 75 goals in their 25 previous league games.
Bastia went ahead in the 19th minute when Diallo headed home at the far post from Gael Danic's cross.
Jardim substituted Tiemoue Bakayoko with Fabinho after the break and the visitors were rewarded seven minutes into the second half when Silva headed home from Almamy Toure's cross.
Radamel Falcao went close to giving Monaco the lead, but his overhead kick went just wide.
Mbappe replaced Valere Germain in the 71st minute but had only one opportunity, being denied by Jean-Louis Leca from close range three minutes from time.
Third-placed Nice will move up to second if they beat Lorient away on Saturday.
(Reporting by Julien Pretot; Editing by Ed Osmond)
Share
