(Reuters) - Mark Wahlberg's dark comedy "Pain & Gain" brought enough box office muscle to knock Tom Cruise out of the No. 1 spot on movie charts in the United States and Canada.

Another box office heavyweight, Robert Downey Jr., scored big overseas with the international debut of Marvel superhero sequel "Iron Man 3."

"Pain & Gain" took in $20 million at U.S. and Canadian theaters over its first three days, according to studio estimates released on Sunday. Cruise's sci-fi thriller, "Oblivion," slipped to second place with $17.4 million.

"Iron Man 3" hauled in $195.3 million in 42 international markets, distributor Walt Disney Co said, a total that surpassed the international opening of "The Avengers." The movie arrives in the United States and Canada on Friday to kick off Hollywood's lucrative summer blockbuster season.

Receipts for "Pain & Gain" beat pre-weekend forecasts for a debut of at least $15 million. The film is based on the real-life story of Miami bodybuilders who kidnap a wealthy deli owner and plan to steal his fortune. When their plot goes awry, the criminals scramble to escape being caught.

"We were estimating high teens, so anything with a two in front is good," said Don Harris, president of domestic theatrical distribution at Paramount Pictures, the Viacom Inc unit that released the movie.

Paramount Pictures produced "Pain & Gain" for $26 million. Dwayne Johnson stars alongside Wahlberg in the film, which is directed by Michael Bay of the blockbuster "Transformers" series.

"Oblivion," a post-apocalyptic drama about the last humans on Earth, brought its two-week total in North America (the United States and Canada) to $64.7 million. Comcast Corp's Universal Pictures estimated international sales through Sunday at $134.1 million, bringing the film's worldwide total to $198.8 million.

Baseball drama "42," about Jackie Robinson's debut as Major League Baseball's first black player, finished in third place with $10.7 million domestically.

In fourth place, new romantic comedy "The Big Wedding" earned $7.5 million. Despite a big-name cast including Robert DeNiro, Susan Sarandon and Katherine Heigl, the movie was ravaged by critics. Only 6 percent of reviews on the Rotten Tomatoes website recommended the film.

Lions Gate Entertainment Corp distributed "The Big Wedding," and Millennium Films covered most of the $35 million production cost.

In the No. 5 slot, animated Stone Age comedy "The Croods" grossed $6.6 million.

North American ticket sales for all movies this year reached nearly $2.9 billion, running 11.8 percent behind sales at the same point in 2012, according to the box office division of Hollywood.com.

The release of "Iron Man 3" next weekend is expected to jump-start domestic sales. Boxoffice.com is projecting $151 million in North American receipts over the film's first three days, which would rank as the biggest opening so far this year.

Disney's executive vice president for motion picture distribution Dave Hollis declined to make a prediction for the film's U.S. opening, but was optimistic based on the overseas numbers.

"To say that we are encouraged by these results is an understatement," Hollis said.

"Oblivion" was distributed by Universal Pictures, a unit of Comcast Corp. Time Warner Inc's Warner Bros studio released "42," while "The Croods" was produced by Dreamworks Animation and distributed by 20th Century Fox, a unit of News Corp.