A very good $73 million dollars assured that the new apes film would be big and it not only far out grossed the rest of the box office but out grossed it predecessor.
Rise of the Planet of the Apes $55 million on it's American opening, it was a (nearly) new franchise so that may have effected it, Dawn has had very positive reviews and Rise was considered a big hit in the end.
Falling into the runner up spot this week is Transformers: Age of Extinction, two weeks at the top has earned it over $200 million in the US.