Monaco had scored 76 times in 26 games before the trip to Guingamp but found chances at a premium with Polish defender Kamil Glik's 24th-minute goal their only reward of an even first half.
Guingamp commanded plenty of possession in the second period before Monaco's Brazilian midfielder Fabinho converted a penalty in the 86th minute to all but seal their 19th Ligue 1 victory of the season.
Etienne Didot pulled a late consolation back for the hosts but Monaco held on for victory to climb three points clear of second-placed Nice who beat Montpellier 2-1 on Friday.
Later on Saturday, Angers SCO host Bastia, Toulouse visit AS Nancy-Lorraine, Lille face Girondins Bordeaux and Stade Rennes play FC Lorient.
Third-placed Paris St Germain, who are six points adrift of Monaco, travel to Olympique de Marseille on Sunday as they continue their bid for a fifth successive French title.
(Reporting by Tom Hayward, editing by Ed Osmond)
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