Tony Stark piloted to the top of the box office but not the record books. "Iron Man 2," the sequel starring Robert Downey Jr. as Marvel's gadget-happy billionaire superhero, earned $133.6 million domestically on its opening weekend, according to distributor Paramount Pictures' estimates Sunday. The opening rocketed past the original $98.6 million debut in 2008 and landed the record as the fifth-biggest opening weekend.