Marvel comics adaptation "Iron Man" strong-armed the box office and blasted into elite territory by becoming one of only 10 films ever to gross 100 million dollars in its opening weekend, industry data showed Sunday.

The estimated 104.25-million-dollar debut marked the eighth most successful opening ever, according to preliminary figures from Exhibitor Relations, and set the stage for a potentially dominant franchise which mimics "Spider-man", whose third movie in the series holds the all-time richest debut.

It marked a spectacular opener for the film version of the comicbook super-hero and burnished the screen credentials of once-troubled Oscar nominee Robert Downey Jr, who as eccentric billionaire Tony Stark invents a powerful armored suit that helps him save the world.

Trailing a distant second, with a debut estimated weekend take of 15.5 million dollars, was romantic comedy "Made of Honor," which stars Patrick Dempsey and Michelle Monaghan as platonic friends who inch towards love as they plan Monaghan's marriage to another man.

Slipping to third place was last week's box office topper "Baby Mama," a surrogate motherhood comedy starring former Saturday Night Live comedians Tina Fey and Amy Poehler, which netted 10.3 million dollars.

In fourth place with 6.1 million dollars was "Forgetting Sarah Marshall," billed as "the world's first romantic disaster comedy," starring British comedian Russell Brand.

"Harold and Kumar Escape Guantanamo" took fifth spot with 6.0 million dollars. The sequel to 2004 "Harry and Kumar go to White Castle" sees stoner buddies landing in the notorious Guantanamo jail after being mistaken for terrorists on a plane.

"The Forbidden Kingdom," the first movie pairing of martial arts legends Jackie Chan and Jet Li, dropped from third to sixth spot on its second weekend, with 4.2 million dollars.

"Nim's Island," a youth-oriented tropical adventure with Jodie Foster and Abigail Breslin, took seventh place with an estimated 2.8 million dollars.

"Prom Night," a remake of a 1980 horror film, carved out 2.5 million dollars to take eighth spot, three weekends after it topped the charts.

In ninth place was gambling drama "21," another former box-office topper which won 2.1 million dollars.

Rounding out the top 10 was "88 minutes," starring Al Pacino as a college professor and part-time FBI psychiatrist hunting down a killer.