Tropic Thunder is still thundering at the box office!

The surprise is not that Tropic Thunder is #1, is that "The Dark Knight" went from 4 to 3 in a comeback! Can it become #1 in the all time list?

LOS ANGELES (Reuters) - Action film parody "Tropic Thunder" held onto the top spot at the North American box office for a third straight week as the summer moviegoing season drew to a close, Hollywood studios reported on Sunday.

Paramount Pictures' farcical combat movie within a comedy, starring Ben Stiller, Robert Downey Jr. and Jack Black, sold an estimated $11.5 million in U.S. and Canadian tickets Friday through Sunday to bring its three-week tally to $83.8 million.

Its biggest competition came from a real action flick, the sci-fi thriller "Babylon A.D." from 20th Century Fox starring Vin Diesel, which grossed an estimated $9.7 million in its first weekend to land at No. 2.

Blockbuster Batman sequel "The Dark Knight" climbed a notch up the box office chart to No. 3 with weekend receipts of nearly $8.8 million, pushing its cumulative domestic haul past the $500 million mark in its seventh week of release.

"Dark Knight," a Warner Bros, release, stands as the second-highest-grossing domestic film of all time, behind "Titanic."

The U.S. Labor Day holiday on Monday marks the official conclusion to Hollywood's 18-week summer film season, which is expected to end with roughly $4 billion in domestic box office receipts overall.

Paramount is a unit of Viacom Inc, Fox is a division of News Corp and Warner Bros. belongs to Time Warner Inc.