'The Help'

Aptly, moviegoers celebrated Labor Day weekend by watching a film about underappreciated household workers. For the third-straight weekend, period dramedy 'The Help' was the top movie at the box office, ending the summer season by fending off three more action-packed newcomers: 'The Debt,' 'Apollo 18' and 'Shark Night 3D.'

From Friday to Sunday, 'The Help' earned an estimated $14.2 million, a microscopic dip of just 2 percent from last weekend. That's almost unprecedented for a movie in its fourth week of release. Credit the fact that the movie added 65 more screens this weekend (for a total of 2,843), along with the weakness of the competition. Over the full holiday weekend, the film earned an estimated $19.0 million, for a four-week total of $123.4 million.

'The Debt'

'The Debt' surprised experts by opening in second place. The Helen Mirren spy thriller had the strongest reviews of the three new wide-release movies, but it also had the fewest screens, just 1,826. Still, as a smart, grown-up thriller, it had strong appeal for older audiences (76 percent of whom were over 35, according to studio polling), which helps explain why it didn't generate the online buzz that's a key predictor for box office tea-leaf readers. They expected 'The Debt' to open in the $7 to $8 million range over the four-day weekend, but it surpassed that by Sunday with an estimated $9.7 million. Over the full holiday weekend, it earned an estimated $12.6 million. Its six-day total, since opening last Wednesday, comes to $14.5 million.

'Apollo 18'

In a close race for third, 'Apollo 18' and 'Shark Night 3D' were separated by just $400,000 according to four-day estimates, with 'Apollo 18' having a slight edge as of Monday with $10.7 million, compared to $10.3 million for 'Shark Night.' (The Friday-to-Sunday race was even closer, with the astronauts edging out the maneaters $8.70 million to $8.64 million.) It wasn't supposed to be that close. 'Apollo 18' opened on 500 more screens than 'Shark Night' and was expected to earn as much as $15 million for the weekend. But it was poorly reviewed and lacked the bikini factor of 'Shark Night,' which was competing for essentially the same audience.

'Shark Night 3D'

Opening in fourth place with an estimated $10.3 million over four days, 'Shark Night 3D' underperformed as well, but not by much; pre-weekend predictions had it opening around $11 or $12 million. Opening in the same late-summer slot where 'Piranha 3D' succeeded last year, 'Shark Night' had a couple of additional advantages. First, it was rated PG-13, not the restrictive R that marked 'Piranha.' (Though some would say the PG-13 rating was just as much a deterrent.) Second, some 80 percent of its screens were 3D, so viewers had little choice but to pay the surcharge.

Rounding out the top five was 'Rise of the Planet of the Apes,' still holding up well in its fifth weekend. From Friday to Sunday, it earned an estimated $7.8 million, down just 12 percent from last weekend. Its four-day total was $10.3 million - much better than the predictions of about $7 million for the whole holiday. To date, 'Apes' has earned $162.5 million.

The summer ended with domestic box office receipts down half a percentage point from last summer, at $4.19 billion compared to. 2010's $4.21 billion. Attendance was down as well, some 1.6 percent, with sales of 525.5 million tickets sold compared to 534.2 million last summer. That makes four summers in a row of declining attendance.

'The Help': Trailer No. 1

The full top 10 (four-day totals):
1. 'The Help,' $19.0 million (2,843 screens), $123.4 million total
2. 'The Debt,' $12.6 million (1,826), $14.5 million
3. 'Apollo 18,' $10.7 million (3,328), new release
4. 'Shark Night 3D,' $10.3 million (2,806), new release
5. 'Rise of the Planet of the Apes,' $10.3 million (3,193), $162.5 million
6. 'Colombiana,' $9.4 million (2,614), $24.0 million
7. 'Our Idiot Brother,' $7.1 million (2,555), $17.3 million
8. 'Spy Kids: All the Time in the World,' $6.6 million (3,007), $31.0 million
9. 'Don't Be Afraid of the Dark,' $6.1 million (2,780), $17.6 million
10. 'The Smurfs,' $5.6 million (2,706), $133.6 million

Follow Gary Susman on Twitter: @garysusman.

Photos: DreamWorks ('The Help'), Focus Features ('The Debt'), The Weinstein Company ('Apollo 18'), Incentive Film Procudtions ('Shark Night 3D')