The Legend Of Tarzan and The BFG were no match for Finding Dory at US cinemas over the July 4th weekend.
The Pixar sequel - featuring the voice of Ellen DeGeneres as the forgetful blue fish - led the box office for the third straight weekend.
According to studio estimates on Sunday, Finding Dory earned $41.9 million (£31.5 million) in North America. Disney is forecasting a four-day holiday haul of about $50 million (£37.7 million).
Of the three debuts, Tarzan came the closest to dethroning Dory with $38.1 million (£28.7 million).
The horror sequel The Purge: Election Year opened solidly with $30.9 million (£23.2 million), in line with previous Purge installments.
The continued success of Dory bit into the opening of Steven Spielberg's Roald Dahl adaption, The BFG.
The movie had a disappointing opening, taking just $19.6 million (£14.7 million).