LOS ANGELES (AP) – Mark Wahlberg is showing some box office muscle. “Pain and Gain” opens at number-one this weekend with $20 million. Wahlberg, Dwayne Johnson and Anthony Mackie are playing knuckle-headed body builders. Tom Cruise’s “Oblivion” drops to second, followed by the Jackie Robinson biopic “42.” The all-star comedy “The Big Wedding” tanks with a fourth-place opening. But the big movie of the weekend isn’t even playing in the U.S. yet. “Iron Man 3” takes in more 195 million in 42 overseas markets. It opens in the States Friday.