EPTFirst was when Bisu attacked the bottom left base with five slow zealots, saw one sunken and decided to go in. Zero pulled off a very successful drone drill that made the zealots look completely inferior. It seemed to me like he had figured out a strong configuration in which he could entrap the zealots and crush them seemingly with ease, and I strongly doubt Bisu expected it to be that powerful. After that failed attack Zero didn't rebuild the sunken because he figured the expansion looked safe enough.
Later Bisu tried to sneak a DT into the main base. Again Zero pulled off an incredible drone drill that completely disabled the DT. Bisu just barely couldn't make it escape that trap and it was killed off before it could do any sort of damage.
After those two failed attempts Zero figured he was so much ahead in supply that he should pump out a lot of hydras and go for a killing blow. At that point it didn't look like Bisu stood a realistic chance anymore. He hunted down overlords with sairs and also tried to kill the remaining one at his natural to save the game with a lone DT, but Zero's forces were too overwhelming.
This didn't look like a game that Bisu lost unavoidably. It was a game that Zero won with very precise play. He was very well prepared for everything that Bisu threw at him. Bisu didn't have an answer to it and he didn't get lucky when it mattered the most (talking about the second drone drill disabling his DT). Had Zero been only slightly less well prepared or if his reaction time was only slightly off, he could've lost this game.
What people often fail to realize is that, at the top level, the difference between a win and a loss is sometimes a split second reaction or a detail in the preparation.
