Neill Blomkamp’s “Chappie” and “Unfinished Business” with Vince Vaughn added up to a weekend to forget at the U.S. box office.

Overall ticket sales plunged as “Chappie,” a science-fiction adventure about a sentient robot, topped charts with a weak $13.3 million from 3,201 locations. Going into the weekend, Sony Pictures was aiming for a debut of roughly $15 million and some analysts expected the film could hit $20 million. Reviews were tepid, and the picture is the latest in a long line of R-rated new releases such as “Fifty Shades of Grey” and “Focus,” which may have hurt it with moviegoers looking for something that appeals to kids as well as adults.

“There’s been a glut of R-rated movies starting from the first of the year,” said Rory Bruer, Sony’s worldwide distribution chief. “I think there’s some R-rated fatigue.”

The odds may have been against “Chappie” from its inception. Original science-fiction films have had a rocky go of it at the box office of late, with “Seventh Son,” “Jupiter Ascending” and “Project Almanac” all crashing on the shoals of audience indifference. Blomkamp may be on safer ground with his next project, a new installment in the “Alien” franchise.

“Chappie” was produced for $49 million, and Sony isn’t ready to concede defeat on the picture just yet, predicting it could make a profit when foreign markets are taken into account. Bruer notes that Blomkamp’s previous films, “District 9” and “Elysium,” were able to stick around for a long time after their debuts.

“The movie plays well, and the uniqueness of the characters is going to drive a conversation that I do believe will help the film in the coming weeks,” he said.

It was a dispiriting weekend overall for the business, with ticket sales down roughly 35% from the year-ago period — a weekend that saw the debuts of “300: Rise of an Empire” and “Mr. Peabody and Sherman.” That also took a chunk out of the substantial lead that the exhibition industry had maintained over 2014’s first quarter numbers. Ticket sales are now up roughly 5% over the previous year’s, but two weeks ago they topped them by roughly 10%.

“The market has been so strong lately, I’m not surprised to see such a big down weekend,” said Phil Contrino, vice president and chief analyst at BoxOffice.com. “Things have to slow down at some point.”

“Chappie” fared better than “Unfinished Business,” another R-rated whiff. The business trip comedy eked out a gloomy $4.8 million across 2,777 locations. It ranks as the lowest debut of Vaughn’s career, raising serious questions about his appeal. The “Wedding Crashers” star has headlined an array of flops over the past four years, including “The Dilemma,” “Delivery Man,” “The Internship” and “The Watch.” A lot is riding on the second season of “True Detective” to return Vaughn to audiences’ good graces.

Twentieth Century Fox distributed the $35 million film, which New Regency financed. The opening crowd for “Unfinished Business” was 55% male and 54% over the age of 25.

“Sometimes this happens where a film doesn’t connect with an audience,” said Spencer Klein, executive vice president of theatrical distribution at Fox. “Fortunately, this hasn’t happened too often to us.”

There was one diamond in the crop of dinged-up new releases — “The Second Best Exotic Marigold Hotel.” The comic tale of retirees making new lives for themselves in India bowed to a sterling $8.6 million across 1,573 locations. Fox Searchlight is distributing the comedy which was co-produced by Participant Media and cost a mere $10 million to produce.

“This audience of moviegoers wants to see something different, and there hasn’t been much out there for them,” said Frank Rodriguez, senior vice president of distribution at Fox. “This market of specialty crowds and more mature audiences has been underserved.”

“The Second Best Exotic Marigold Hotel” will add approximately 300 screens to its current crop of venues next weekend, Rodriguez predicted. The first picture stuck around for months, eventually making $46.4 million, but this film had a wider debut and should be more front-loaded. The film played older and female, with more than 65% of the crowd comprised of women and the same percentage over the age of 50.

“Our core audience came out this weekend, but it’s comprised of moviegoers who don’t always rush out immediately,” said Rodriguez. “We think this is the kind of film that could stick around.”

Last week’s champ, the Will Smith heist picture “Focus,” had to settle for runner-up status, taking second place on the charts with $10 million. That brings the film’s take to $34.6 million.

Among holdovers, “Kingsman: The Secret Service” took in $8.3 million, pushing its take to $98 million, while “Fifty Shades of Grey” added $5.6 million to its $156.4 million haul. “The SpongeBob Movie: Sponge Out of Water” continued to benefit from being one of the only family-friendly releases in the market, picking up $7 million and driving the picture to $149 million at the Stateside box office.

At the arthouse, Sony Pictures premiered the spin-doctor documentary “Merchants of Doubt” on four screens where it earned $20,327, while “The Hunting Ground,” a look at sexual violence on college campuses, added $8,936 from two screens to its $45,822 gross.

Roadside Attractions and Black Label Media’s critically adored thriller “71” capitalized on good reviews, earning $70,590 after expanding from four to 16 screens in New York and Los Angeles.

Next weekend brings Disney’s live-action version of “Cinderella” and with it a chance at box office redemption.