The Gers boss Steven Gerrard was full of praise for striker Alfredo Morelos, who was signed by Pedro Caixinha in the summer of 2017, for his contribution in the game.
Rangers struggled to break the St Mirren defence, and it took 80 minutes for them to break the deadlock.
Daniel Candeias opened the scoring for Rangers, and Morelos added another to seal all three points for Rangers.
Morelos scored 18 goals in all competitions for the Gers last season. The Colombian international is looking to surpass that mark comfortably, as he has now notched 14 goals already this season.