The Disney tentpole's North American debut is bested only by Marvel pic " The Avengers "; the threequel has taken in a massive $504.8 million internationally, led by China with $63.5 million. Kicking off the season with the pedal to the metal, Robert Downey Jr.'s Iron Man 3 made the record books as it opened to $175.3 million from 4,253 theaters in North America, the No. 2 debut of all time behind fellow Marvel pic The Avengers ($207.4 million), also starring Downey as Iron Man. Iron Man 3 received a glowing A CinemaScore from audiences, fueling word of mouth. Overseas, the Disney and Marvel threequel grossed $175.9 million in its second weekend, putting the 3D movie's international total at $504.8 million and early worldwide haul at $680.1 million. Internationally, Iron Man 3 - the first title in the franchise to be released in 3D -- is all but matching Avengers overseas, where 3D remains a big draw. China leads with a whopping $63.5 million, the top op