Carter, the world number 15, pulled a frameback just before the interval to make it 3-1, but gifted his opponent too many opportunities to win another.
Chile now needed just one more goal to put themselves back in the frame to finish top, but Spain had just enough about them to take advantage of the extra man.
But O'Sullivan responded with the first century of the match, and after Maguire had grabbed another frameback with a run of 57, the favourite roared to victory with another fluent display of potting.