The girls are back in town. Sex and the City, the romantic comedy, based on HBO’s long-running television series of the same name, unexpectedly overtook the latest Indiana Jones at the domestic box office, bringing in an estimated $55.7 million since opening with midnight shows on Thursday, according to Warner Brothers., which released the film.

The performance fell short of the $70 million-plus opening some foresaw after sellout crowds — 85 percent of the ticket buyers women, many viewing in groups — brought the film about $26 million in sales on Friday. Still, the weekend opening far exceeded industry expectations.

“It is kind of mind-boggling,” Sarah Jessica Parker, the Sex and the City star, said in a telephone interview from her Manhattan home on Saturday. “We are thrilled and humbled the audience came out.”Sex and the City, of course, benefited from the enormous audience awareness that came with the television series’ six seasons, strong DVD sales and continuing appearances in syndication on TBS. There was also no shortage of media attention showered on the return after four years of Carrie, Miranda, Samantha and Charlotte, whether features about their clothes, their men or the show’s enduring influence (for good or ill) on the culture.

And yet surprise at the weekend performance was palpable. Parker, for instance, said she did not intend to sit home this weekend monitoring the box office results. But by late Friday, fans were sending messages and even photographs to her cellphone of women in line outside movie theatres across the country. (As the weekend went on, more men showed up, according to Warner Brothers.) A clutch of negative reviews did nothing to dampen the thirst for making it at the theatre.

“It’s a cultural phenomenon; it’s an absolutely incredible opening,” said Dan Fellman, Warner’s president for theatrical distribution, speaking by phone on Sunday. First-weekend ticket sales, he noted, were far beyond those of other R-rated comedies, including American Pie 2 from Universal Pictures in 2001 and The Wedding Crashers from New Line Cinema in 2005. Parker credited Michael Patrick King, the movie’s writer and director, with creating an update of the hit HBO television show that brought the characters forward. “It’s a movie about being a grown-up,” she said. Whether the rest of the summer’s entrants will excite moviegoers as much as last year remains to be seen, but one thing is certain: The success of Sex and the City will spark immediate talk of a sequel. “They might be talking about a sequel,” Parker said. “But it still feels like we’re opening this movie.”