It couldn't last forever. Eventually someone had to knock The Dark Knight off of the box office throne. Last weekend Pineapple Express took a crack at it (well more of a pot shot really (I know, I know, bad pun) but couldn't muster quite the cash. Now as Batman heads into his fifth weekend, attendance may have finally dwindled enough for someone to topple him.

After a weak start in early release Wednesday, Tropic Thunder got a kick start heading into the weekend. Friday's ticket sales showed the star-studded comedy climbing somewhat, making $8 million first night out. It's not enough to suggest the movie will be a box office smash, but probably enough to beat The Dark Knight. There's one thing standing in its way... Batman's tendency to smack down the new debuts come Saturday.

For the last three weekends The Dark Knight's sales have jumped from Friday to Saturday by 20% to 40%, while the closest competition has significantly dropped. This is Knight's fifth weekend out and on Friday it came in with only $5 million, giving Tropic Thunder a solid lead. Thanks to that it might be premature to count Batman out just yet, but after a rare four-weekend run at number one, Gotham's hero may finally see number two...or maybe even number three.

Star Wars: The Clone Wars also debuted and at $6 million it just might float on top of Dark Knight as well, though hope there is a little sketchier. Besides, it has bigger problems. With slim hope of breaking $20 million over the weekend it could face be in danger of not turning a profit for Lucasfilms. Not that they're short of money over there, but if this movie is intended to be the kick-off for a new branch of Star Wars animated TV series, there's a good chance studios might be giving that idea a second thought.