LOS ANGELES -- Ben Stiller comedy "Tropic Thunder" earned the top slot at the North American box office for the third straight weekend, but it was "The Dark Knight" that stole the show by reaching the $500-million mark, industry figures showed Sunday.

Stiller's movie-within-a-movie, about a group of actors shooting a war film in the middle of a real-life conflict zone, scooped $11.5 million from Friday to Sunday in the US and Canada, totaling $83.8 million since its opening, according to preliminary figures by box-office tracker Exhibitor Relations.

But the week's highlight was reigning summer blockbuster "The Dark Knight," the Batman sequel which with a third place take of $8.75 million pushed its total domestic haul to more than $502 million, only the second film in history -- after James Cameron's "Titanic" -- to top the half-billion-dollar mark.

Debuting at second place was ?Babylon A.D.,? a sci-fi action thriller starring Vin Diesel and Michelle Yeoh which earned $9.7 million.

Slipping two places to fourth with $8.3 million was the comedy "The House Bunny," about an ousted Playboy bunny who becomes the house mother at a dysfunctional college sorority.

In at fifth with $7.9 million was another debut, "Traitor," a war-on-terror epic featuring Don Cheadle as a former US Special Ops officer and potential international conspirator.

"Death Race," a futuristic action-adventure flick starring Jason Statham as an ex-convict forced to compete against prison inmates in a brutal, freedom-or-death car race, raked in $6.2 million for sixth place.

Debuting at seventh with $6.2 million was the natural disaster spoof "Disaster Movie," about a band of bunglers struggling to survive as the world comes to an end. The ill-timed film opened as the US Gulf Coast faces the imminent wrath of Hurricane Gustav.

Holding on to eighth place was the Abba musical remake "Mamma Mia!" with $4.4 million, for a total seven-week take of $131.5 million, followed by marijuana comedy "Pineapple Express," starring Seth Rogen and James Franco, which earned $3.5 million.

Rounding out the top 10 was Woody Allen's latest film, the romantic comedy "Vicky Cristina Barcelona," with $3.0 million.