Related על מגילה 33:21

One who reads the Megillah out of order does not fill [his obligation], and so too with Hallel and so too with tefillah (i.e., the Amidah), and so too with the recitation of the Shema. [If] the [public] reader of the Megillah errors or skips over one of its verses, he does not go back and read the verse by itself, but he begins from the same verse and continues until the very end [of the Megillah], and so too with Hallel, and so too with tefillah, and so too with the recitation of the Shema. One who enters the synagogue and found that they had [already] read half [of the Megillah], and he finishes with them, he does not go back and read it from the beginning until the place [where they were when he arrived], but rather he starts from the beginning and continues until the very end, and so too with Hallel, and so too with tefillah, and so too with the recitation of the Shema.