Mathys Detourbet opened the scoring in the 33rd minute before substitute Matthis Abline sealed the victory with a stoppage-time strike, giving the French side a third consecutive win in the competition.
Monaco made the breakthrough after Takumi Minamino delivered a pass across the penalty area for Detourbet, who finished from close range to register his first goal for the club since joining on loan from Manchester City.
Nordsjaelland struggled to create meaningful opportunities in the first half, with their best opening falling to defender Victor Nelsson, whose header from a corner failed to trouble the Monaco defence.
The hosts thought they had extended their advantage early in the second half when Paris Brunner found the bottom corner, but the effort was ruled out for offside.
Minamino also had a goal disallowed after turning home Detourbet’s cross, with the Japanese forward caught offside.
Monaco continued to dominate the attacking moments. Folarin Balogun missed a good opportunity when he headed straight at goalkeeper Andreas Hansen from close range, while Minamino later forced another save with a volley.
Nordsjaelland, meanwhile, struggled to test Monaco goalkeeper Lukas Hradecky as they searched for an equaliser.
The visitors' resistance finally ended in stoppage time when Detourbet played Abline through on goal. The substitute kept his composure to find the bottom corner and confirm the 2-0 victory.
The result gave Monaco three wins from their opening three Conference League matches, marking their first three-match winning start to a major European campaign in 30 years.
Nordsjaelland remained without a victory in the league phase, having recorded two draws and one defeat.
Result: Monaco 2-0 Nordsjaelland
Goals:
• Monaco: Mathys Detourbet 33', Matthis Abline 90+1'