First, props to Freddie Roach. Who expected Manny to come out slinging right hooks? Mr. Roach had identified an Hatton trait of "studying his right," and helped his fighter develop a strategy to exploit it.
Second did you notice that, when Manny landed the decisive left, he was not watching the target? His head was down, slipping a punch. I guess its like a skillful guitar who doesn't have to look at the fretboard to know where the notes are.