Calum Gallagher and Stephen Mallan scored second-half goals to earn St Mirren the points in a 3-1 win over Morton in the Scottish Championship.The Buddies had been on course for a routine win after Lawrence Shankland's 10th goal of the season put them ahead early on when he struck into the top corner from distance.But Morton hauled themselves level in the 58th minute when Denny Johnstone fired into the bottom corner from the edge of the area.That parity was short-lived, though, as Gallagher stroked home into the bottom corner just two minutes later.Mallan made sure of the points in added time when he produced a composed finish.