LOS ANGELES – “The Chronicles of Narnia: Prince Caspian” dethroned “Iron Man” as ruler at the box office, pulling down $56.6 million, according to studio estimates Sunday.

The Walt Disney Co.’s action sequel took in less domestically in its opening weekend than “The Chronicles of Narnia: The Lion, The Witch and the Wardrobe,” which sold $65.6 million in North America in its debut weekend in December 2005. “Caspian” also raked in $20.7 million overseas.

But Disney expects the PG-rated movie, based on the C.S. Lewis fantasy series, to ride high through the coming Memorial Day weekend. The first “Narnia” tale grossed $745 million worldwide over its theatrical run.

“This is a film that we think is going to play all summer long and it’s got nothing but school holidays in front of it,” said Mark Zoradi, president of the Walt Disney Studios Motion Picture Group.

Disney is in pre-production on the third of the series, “The Chronicles of Narnia: Voyage of the Dawn Treader,” set for release in the summer of 2010.

Marvel Studios’ “Iron Man” slipped to second place after two weeks at No. 1 with $31.2 million, bringing its domestic total to $222.5 million.

Paul Dergarabedian, president of tracking firm Media By Numbers LLC, said the flawed superhero flick is holding its appeal better than “Spider-Man 3” did the previous May.

“‘Iron Man’ continues to hold very well,” he said. “It’s definitely cutting into audiences across the board.”

The 20th Century Fox comedy “What Happens in Vegas,” starring Cameron Diaz and Ashton Kutcher, came in third, with $13.9 million in its second weekend. Its domestic total reached $40.3 million, well above its $35 million budget.

“It’s clearly the comedy, non-family movie in the marketplace right now,” said Chris Aronson, a Fox senior vice president.

Warner Bros.’ disappointing “Speed Racer” slowed to $7.6 million for fourth place, driving in $29.8 million over two weeks.

The studio said it was not ready to call it game over on the Wachowski brothers movie, which cost $120 million to make.

Jeff Goldstein, Warner Bros.’ executive vice president of distribution, said next weekend was “do or die” for the movie.

Overture Films’ acclaimed drama, “The Visitor,” crept into 10th place at the box office with $687,000.

The distributor picked up the indie film, about a professor who discovers a couple living in his little-used New York apartment, at the Toronto Film Festival for a reported $1 million. It has grossed $3.4 million so far.

“It’s good to know that you don’t have to have special effects in your movie to make money,” said Overture Films’ senior vice president Adam Keen.

“Indiana Jones and the Kingdom of the Crystal Skull,” which received a somewhat ho-hum reaction at the Cannes Film Festival on Sunday, whips its way into theaters on Thursday.

Estimated ticket sales for Friday through Sunday at U.S. and Canadian theaters, according to Media By Numbers LLC. Final figures will be released Monday.