LOS ANGELES — Audiences hit the road with Robin Williams as his family vacation romp "RV" opened at No. 1 with $16.4 million, while the acclaimed Sept. 11 drama "United 93" debuted with $11.6 million.

Studio estimates Sunday had Universal Pictures' "United 93" in second place, just ahead of Disney's sports comedy "Stick It," which premiered with $11.3 million.

The weekend's other new wide release, Lionsgate's spelling-bee drama "Akeelah and the Bee," was No. 8 with $6.25 million.

The 20th Century Fox release "RV" was expected to debut on top, but "United 93" had been an unknown quantity, with Hollywood analysts wondering whether moviegoers were ready to relive the horrors of the Sept. 11, 2001, terrorist attacks.

"It's not about the positioning of the film. It's about the fact that the American public spoke out," said Nikki Rocco, head of distribution for Universal Pictures. "This is a wonderful result. What they said was that it wasn't too soon for a film about Sept. 11."

Married couples accounted for just over half the "United 93" audience, and 71 percent of viewers were 30 and older, according to Universal.

With painstaking authenticity, "United 93" recounts the horrific end of passengers who fought back against their hijackers aboard one of the commandeered planes, which crashed in rural Pennsylvania.

Shot on a modest budget of $15 million, "United 93" should easily turn a profit once theatrical, television and DVD revenues are tallied. Universal said it will donate 10 percent of the first weekend's grosses to the Flight 93 National Memorial in Pennsylvania.

Playing in 1,795 theaters, about half as many as "RV," "United 93" averaged a solid $6,462 a cinema, the best results among the top-10 movies.

1. "RV," $16.4 million.

2. "United 93," $11.6 million.

3. "Stick It," $11.3 million.

4. "Silent Hill," $9.3 million.

5. "Scary Movie 4," $7.8 million.

6. "The Sentinel," $7.6 million.

7. "Ice Age: The Meltdown," $7.05 million.

8. "Akeelah and the Bee," $6.25 million.

9. "The Wild," $4.7 million.

10. "The Benchwarmers," $4.4 million.