Robert Downey Jr. in Iron Man 2

Iron Man 2 powered to a No. 1 debut over the weekend with $133.6 million for the fifth-biggest opening of all time.

The haul also makes the sequel, starring Robert Downey Jr., the third-biggest superhero-movie debut of all time, behind leader The Dark Knight, which opened to $158 million in 2008, and runner-up Spider-Man 3, which bowed to $151 million in 2007, according to Box Office Mojo. (The Twilight Saga: New Moon, with $142 million, and Pirates of the Caribbean: Dead Man's Chest, with $135 million, are in third and fourth place, respectively, on the all-time list.)

Watch clips from Iron Man 2

Combined with international ticket sales, Iron Man 2's take already stands at $327.6 million.

Landing way behind in second place was A Nightmare on Elm Street, which reeled in $9.1 million. How to Train Your Dragon followed in third place and crossed the $200 million mark with $6.7 million.

The weekend's other new release, the documentary Babies, debuted in 10th with $1.57 million, just behind The Losers ($1.8 million).

DJ AM heads to the big screen in posthumous Iron Man 2 cameo

Rounding out the top 10: Date Night (No. 4, $5.3 million); The Back-Up Plan (No. 5, $4.3 million); Furry Vengeance (No. 6, $4 million); Clash of the Titans (No. 7, $2.3 million); and Death at a Funeral (No. 8, $2.1 million).