LOS ANGELES (AFP) - Marvel comics adaptation "Iron Man" kept a steely grip on the top box office slot for a second week running, industry figures showed Monday, as debutant "Speed Racer" stalled at the start line. "Iron Man," starring Robert Downey Jr as billionaire industrialist Tony Stark who invents an armored suit to help him save the world, raked in 51.2 million dollars, Exhibitor Relations said, for a total of 177.8 million. In second place with a take of 20.2 million dollars was "What Happens in Vegas," a romantic comedy starring Ashton Kutcher and Cameron Diaz as a couple who wake up married after a night of debauchery in Sin City. But it was a disappointing opening for "Speed Racer," the long-awaited first feature film from Wachowski brothers Andy and Larry since their successful trilogy of "Matrix" movies. "Speed Racer," a high-tech live-action take on the Japanese boy-drives-car animated series from the 1960s starring Emile Hirsch as the hero, opened to a disappointing 18.6 million dollars. Slipping two spots to fourth with 8.1 million dollars was another romantic comedy, "Made of Honor," which stars Patrick Dempsey and Michelle Monaghan as friends who inch towards love as they plan her marriage to another man. In fifth was former box office topper "Baby Mama," a surrogate motherhood comedy starring former "Saturday Night Live" comedians Tina Fey and Amy Poehler, which netted 6.2 million dollars. "Forgetting Sarah Marshall," billed as "the world's first romantic disaster comedy," was sixth with 3.8 million dollars. In seventh was "Harold and Kumar Escape from Guantanamo Bay" with 3.1 million dollars. The sequel to 2004's "Harry and Kumar go to White Castle" sees stoner buddies landing in the notorious Guantanamo jail after being mistaken for terrorists. "The Forbidden Kingdom," the first movie pairing of martial arts legends Jackie Chan and Jet Li, dropped from sixth to eighth spot on its third weekend, with 2.2 million dollars. "Nim's Island," a youth-oriented tropical adventure with Jodie Foster and Abigail Breslin, came in at ninth place with 1.5 million dollars. Rounding out the top 10 was "Prom Night," a remake of the 1980 slasher flick starring Jamie Lee Curtis, which took in one million dollars.