Sometimes -- more often than I'd care to admit -- I'm wrong about just how the weekend's box office will play out. But I'm rarely gobsmacked like I am this week. I expected G-Force to be part of the Disney live action also rans -- at best, I thought it would put up Race to Witch Mountain-type numbers; maybe $24 million. And I thought that it would handily be beaten by the well-liked Harry Potter and the Half-Blood Prince, coming off a franchise record opening.

That is not how the estimates have it. As of Sunday, the guinea pig spy movie is ahead of Half-Blood Prince by just over $2 million: $32.2 to Potter's $30. Potter tumbled over 60% from its opening -- actually not the biggest drop-off in series history, which honor belongs, strangely, to Prisoner of Azkaban. Though I wouldn't shed any tears for the folks at Warner Bros., what with the film's worldwide gross breaking $600 million, the drop is a bit of a disappointment for the well-reviewed sixth film. G-Force, I guess, is a triumph for talking CGI animals and 3D.

The Ugly Truth opened strong just below Potter, landing between Katherine Heigl's 27 Dresses and Knocked Upwith $27 million. That's not too far off from the numbers that The Proposal -- considered one of the summer's strongest performers -- put up in June. And Orphan was a horror disappointment with $12.8 million and fourth place, though this likely was not an expensive film. Let me just say that the movie, which I liked, did not have the best marketing campaign, with trailers that seemed to leave little reason to see the movie. (That turned out not to be the case, but you had to actually go see the movie to realize that.)

And down at #11, (500) Days of Summer enjoyed a strong expansion to 85 screens, maintaining a per-screen average of just under $20,000.

Here's the full chart:

1 - G-Force (Disney) - $32.15 ($8,697) - $32.15
2 - Harry Potter and the Half-Blood Prince (Warner Bros.) - $30.00 ($6,936) - $221.83
3 - The Ugly Truth (Sony) - $27.00 ($9,368) - $27.00
4 - Orphan (Warner Bros.) - $12.77 ($4,644) - $12.77
5 - Ice Age: Dawn of the Dinosaurs (Fox) - $8.20 ($2,485) - $171.29
6 - Transformers: Revenge of the Fallen (Paramount/Dreamworks) - $8.00 ($2,471) - $379.09
7 - The Hangover (Warner Bros.) - $6.47 ($2,829) - $247.08
8 - The Proposal (Disney) - $6.42 ($2,311) - $140.09
9 - Public Enemies (Universal) - $4.17 ($1,820) - $88.10
10 - Brüno (Universal) - $2.71 ($1,435) - $56.52
11 - (500) Days of Summer (Fox Searchlight) - $1.63 ($19,176) - $3.00

Next week: The Apatow-riffic Funny People, the not-screened-for-the-press Aliens in the Attic, and the independently-released horror film The Collector.