A system in which gravitation and inertial effects on platen verticality and sagging are compensated by an anti-tilt actuator (68, 70). A hydraulic actuator (68, 70) secured beneath the platen is either set to offset only gravitationally-related sagging of the mold half (60, 62) by providing a compensating upward force (relative to a stable clamp base 80), or otherwise its upward force can be dynamically adjusted also to compensate for swaying or tilting of the mold-platen assembly caused by stroke cylinder (98) operation and related inertia/momentum effects. Preferably, a level sensor (94) measures and communicates a degree of horizontalness/verticality of the platen (48, 50) to a machine controller (88) which, in turn, generates a control signal (87) to cause variation in cylinder pressure in the anti-tilt actuator (68, 70), thereby achieving substantially continuous alignment between the mold halves (60, 62) and reduced component wear.