Second-placed Hibernian scored in stoppage time to draw 1-1 with Falkirk. Lee Miller gave the Bairns the lead in the 84th minute, but they could not hold on as Martin Boyle headed in to give Hibs a share of the points.
Bottom side Alloa Athletic came out on top against relegation rivals Livingston to close the gap between the clubs to three points. Robbie Crawford scored the only goal of the game in the 64th minute to give the Wasps their second win of the season.
Queen of the South drew 1-1 against Raith Rovers yesterday evening.
Results in full: Dumbarton 1-0 St Mirren (0-0), Hibernian 1-1 Falkirk (0-0), Livingston 0-1 Alloa Athletic (0-0), Rangers 2-2 Greenock Morton (1-1)