St Mirren's great escape continued as they boosted their Scottish Championship survival hopes with a 4-1 Renfrewshire derby victory over fourth-placed Morton.Stelios Demetriou, Stephen Mallan, John Sutton and Gary McKenzie netted to lift St Mirren, now unbeaten in seven league games, out of the relegation play-off zone.Demetriou put the visitors ahead in the 18th minute before Andy Murdoch levelled on the half hour, lashing home from Michael Doyle's cutback following a fast break.But St Mirren secured the points as Mallan fired in a low shot shortly after half-time, Sutton slid in to convert on his 100th start and McKenzie headed home late on.