NEW YORK May 5 (Reuters) - Superhero sequel "Iron Man 3" rocketed to the top of U.S. and Canadian box office charts, kicking off Hollywood's summer movie season with an estimated $175.3 million in weekend ticket sales for the second biggest opening of all time.
The movie from Walt Disney Co's Marvel studio stars Robert Downey Jr. as Tony Stark, a billionaire businessman with a superhero alter-ego.
"Iron Man 3" finished behind Marvel's "The Avengers," which debuted one year ago with $207.4 million, and ahead of the July 2011 release of "Harry Potter and the Deathly Hallows - Part 2," which earned $169.2 million over its first three days.
The "Iron Man" mania trounced all other movies. Dark action comedy "Pain & Gain" finished in second place, grossing $7.6 million, according to studio estimates on Sunday. Baseball drama "42" took the No. 3 slot with $6.2 million.
"Pain & Gain" was released by Paramount Pictures, a unit of Viacom Inc. Warner Bros., a unit of Time Warner Inc , distributed "42."