Within first-order phase transitions, we investigate pretransitional effects due to the nonperturbative, large-amplitude thermal fluctuations which can promote phase mixing before the critical temperature is reached fromabove. In contrast with the cosmological quark-hadron transition, we find that the rapid cooling typical of therelativistic heavy ion collider and large hadron collider experiments and the fact that the quark-gluon plasmais chemically unsaturated suppress the role of nonperturbative effects at current collider energies. Significant supercooling is possible in( anearly)homogeneous state of quark gluon plasma.