A carton opening method and assembly for a continuous motion packaging machine directs opposed carton engaging plates perpendicular to opposite side walls of a collapsed carton moving through the opening assembly. A vacuum is applied to the opposed carton side walls when the assemblies engage the carton. One or more of the opposed carton engaging assemblies are retracted to fully open the carton, which is then transferred to a conveyor that transports the carton to the next workstation of the packaging machine. The carton opening operation is accomplished while tracking the carton movement through the carton opening assembly.