If Buddha is able to predict the future of other sentient beings how can freewill be possible as its very nature is that of unpredictability?

It seems to me that prophecy could only be used to predict the most likely outcomes based on the mental states of the beings whose future is being predicted at the time of the prophecy. For instance, there is a scripture I just read in which the Buddha allowed Devadatta to become a monk because if he wasn't allowed to that he would be sent to a rebirth of torment after torment for Aeons but if he entered the Sangha he could considerably cut down on this negative Karma and would eventually become a Buddha whose name the Buddha even predicted. I know freewill is limited based on past karma and the number of choices one has available at any given moment but does the power of prophecy somehow still allow for freewill or is it just a sign of pre-determined fate?