Marvel’s $170 million 3-D sequel Thor: The Dark World topped the box office on its opening Friday, though it proved less mighty than most analysts were expecting.

The film earned $31.6 million yesterday, a 24 percent increase over the original Thor‘s $25.5 million first Friday in 2011. Thor wound up with a $65.7 million opening, and if The Dark World performs similarly it should earn between $75 and $80 million over the Friday-to-Sunday period. That’s certainly not a bad total — but considering Iron Man 3 opened 36 percent higher than Iron Man 2 following The Avengers, it’s pretty disappointing. Audiences issued Thor: The Dark World an “A-” CinemaScore.

In second place, Jackass Presents: Bad Grandpa pulled in another $3.4 million on Friday, which should lead to an $11.5 million weekend. The $15 million Paramount film should have about $79 million total by Sunday night.

Last Vegas scored $3.2 million, which will yield about $11 million for its second weekend. CBS Films’ elderly Vegas comedy will have about $37.5 million against a $28 million budget after this weekend.

Ender’s Game plummeted 70 percent from its first Friday to a weak $2.9 million. The film will earn about $10 million for the weekend — giving it a scary low $43 million in its first ten days. Why is that scary? Because it cost Summit a whopping $110 million to produce.

Rounding out the Top 5 was Free Birds, which flapped away with $2.6 million. The Thanksgiving-themed family film will likely only drop by about 30 percent in its sophomore frame, giving the $55 million film $30 million total.

Check back tomorrow for the full box office report.

Thor: The Dark World

  • Movie
  • PG-13
  • 112 minutes
  • Alan Taylor