The sci-fi thriller, Super 8, opened at #1 at the American box office this weekend, grossing $35.5 million over 3 days, industry data confirmed Monday.

Directed by JJ Abrams, the horror flick takes place in a little Ohio town where a group of children witnesses a train wreck while creating a home movie. Shortly after the crash, unusual events and disappearances start to occur.

Knocked off the leading spot was, X-Men: First Class, which earned $24.1 million for 2nd place. Soon after the prequel’s 2nd week it received a total of $98 million, based on business tracker Exhibitor Relations.

The Hangover: Part II is in 3rd place for estimated weekend sales, with $17.7 million earnings this weekend plus a total of $215.7 million domestically over three weeks.

The box office hit for the summer at this point is, Pirates of the Caribbean: On Stranger Tides, that’s netted $887 million throughout the world in five weeks along with a projected $10.9 million in the United States this weekend, for fifth spot.