Studio estimates Sunday put "Gatsby" at No. 2 behind Robert Downey Jr.'s superhero sequel, which pulled in $72.5 million domestically to raise its total to $284.9 million after just 10 days in U.S. theaters.
With an additional $89.3 million in its third weekend overseas, "Iron Man 3" lifted its international total to $664.1 million and its worldwide haul to $949 million.
"The Great Gatsby" far exceeded expectations by distributor Warner Bros. of a $35 million to $40 million opening weekend.
Director Baz Luhrmann's 3-D adaptation of the F. Scott Fitzgerald classic was a rare box-office smash for films aimed at older adults during the youth-minded summer season. According to Warner Bros., viewers over 25 made up 69 percent of the film's audience.
"It answers the question that you and I hear all the time from people over 50, 'There's nothing for me to see,'" said Dan Fellman, the studio's head of distribution. "While every studio has the $200 million tentpoles in the marketplace, you still have those who feel that it's not directed at them, which is true. So that's why I think counterprogramming like this is very important."
The weekend's other new wide release, Lionsgate's romantic comedy "Peeples," flopped at No. 4 with just $4.9 million. Produced by Tyler Perry, the movie stars Craig Robinson and Kerry Washington in a meet-the-parents-style farce.
Getting a head start on its domestic launch Friday, "Star Trek: Into Darkness" opened with $31.7 million in seven international markets. Its overseas debut included $13.3 million in Great Britain, $7.6 million in Germany and $5.5 million in Australia.
Starring DiCaprio in the title role as 1920s mystery millionaire Jay Gatsby, the latest Fitzgerald update co-stars Carey Mulligan as his lost love and Tobey Maguire as the friend chronicling their doomed romance.
It was by far the biggest debut ever for filmmaker Luhrmann, whose previous best was $14.8 million for "Australia." In just one weekend, "The Great Gatsby" nearly matched the $57.4 million domestic haul that Luhrmann's top-grossing film, the musical "Moulin Rouge!", managed in its entire run.
"Gatsby" also gave DiCaprio his second-biggest debut, behind the $62.8 million take for "Inception."
The film's success follows a bumpy road to theaters. Originally scheduled for release last December, Warner Bros. pushed it back to summer to give Luhrmann more time to finish his elaborate visual spectacle.
How well the film holds up in coming weeks depends on word-of-mouth from fans. Reviews for "The Great Gatsby" have been so-so, with many critics saying it sacrifices drama and substance for style and dazzle, including Lurhmann's elaborate party scenes backed by a contemporary soundtrack featuring Jay-Z, Beyonce and Lana Del Rey.
"Iron Man 3" was down a steep 58 percent from its opening weekend haul, no surprise given that its $174.1 million domestic debut was the second-biggest ever. The only film to do more business was Downey and company's ensemble adventure "The Avengers," which topped $200 million in its premiere last year.
"The Avengers" held up better in its second weekend with $103.1 million, a drop of only 50 percent. But "Iron Man 3" is on its way to becoming the biggest solo superhero hit worldwide and the second-biggest comic-book adaptation, behind the $1.5 billion "Avengers" payday.
"This is on a trajectory like no other individual superhero movie we've ever seen," said Paul Dergarabedian, an analyst for box-office tracker Hollywood.com. "In less than three weeks, this thing is honing in on a billion dollars. It's just a testament to the incredible popularity of this character."
The movie already has far surpassed the franchise best of $624 million worldwide for "Iron Man 2."
Estimated ticket sales for Friday through Sunday at U.S. and Canadian theaters, according to Hollywood.com. Where available, latest international numbers are also included. Final domestic figures will be released Monday.
1. "Iron Man 3," $72.5 million ($89.3 million international).
2. "The Great Gatsby," $51.1 million.
3. "Pain and Gain," $5 million.
4. "Peeples," $4.9 million.
5. "42," $4.7 million.
6. "Oblivion," $3.9 million ($11.7 million international).
7. "The Croods," $3.6 million ($17.3 million international).
8. "The Big Wedding," $2.5 million ($2 million international).
9. "Mud," $2.4 million.
10. "Oz the Great and Powerful," $802,000.