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It took six weeks, but "Black Panther" has finally been unseated as the top film at the North American box office. The monsters vs. robots science-fiction sequel "Pacific Rim: Uprising" dethroned the superhero sensation with $28 million in ticket sales over the weekend, according to studio estimates Sunday.

But the result for "Pacific Rim: Uprising," a Universal Pictures-Legendary Entertainment release that cost $150 million to make, was soft — at least domestically. Like the recently released "Tomb Raider," its biggest business was in China. "Pacific Rim: Uprising" made its debut there with $65 million for Legendary, which the Chinese conglomerate Wanda Group acquired in 2016.

A scene from "Pacific Rim: Uprising." Legendary Pictures / Universal Pictures via AP

And even though "Black Panther" slid to second place in its sixth weekend, with $16.7 million, Ryan Coogler's film notched another box office milestone. It's now the highest-grossing superhero film ever in North America, not accounting for inflation. The film's $631 million in domestic ticket sales has surpassed the $623 million of 2012's "The Avengers."

"Black Panther" also becomes the fifth-highest-grossing film of all-time, above "Star Wars: The Last Jedi."

The record-breaking hit of "Black Panther" has been followed by a string of lackluster performers, including "Tomb Raider," "A Wrinkle in Time" and "Red Sparrow."

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"Pacific Rim: Uprising" may have taken down the champ, but a blockbuster heir to "Black Panther" has yet to be found. Next weekend, Steven Spielberg will try with his big-budget virtual reality spectacle "Ready Player One."

Hollywood has essentially already squandered the early lead "Black Panther" gave it. Despite the firepower of "Black Panther," the year is running 2.6 percent behind 2017 at U.S and Canadian theaters, according to comScore. This weekend was down by 36.5 percent from last year, when "Beauty and the Beast" was in its second week and the surprisingly successful "Power Rangers" made its debut.

"One movie isn't enough to support a whole marketplace," said Paul Dergarabedian, a senior media analyst for comScore. "We need a real shot in the arm here. 'Pacific Rim,' that's a fine opening. But we need bigger numbers to be put up."

MGM and Paramount Pictures' animated family sequel "Sherlock Gnomes" disappointed, with a $10.6 million debut. Forecasts had been higher for the sequel to "Gnomeo & Juliet," which grossed $194 million worldwide in 2011.

The results were also modest for Steven Soderbergh's "Unsane," a psychological thriller starring Claire Foy ("The Crown") that the director shot with iPhones. The Bleecker Street-Fingerprint Releasing film opened with $3.9 million in 2,023 theaters. Although both were inexpensively made, neither of Soderbergh's first two films following his brief retirement from Hollywood has made much of a dent at the box office. Last year's "Logan Lucky," starring Channing Tatum, tapped out at $27.8 million domestically.

But there were also bright spots. The Christian drama "I Can Only Imagine" held especially strong in its second weekend. The Lionsgate-Roadside Attractions release grossed $13.8 million, bringing its two-week total to $38.5 million.

"I Can Only Imagine" has emerged as the clear faith-based film of choice ahead of Easter, likely to the detriment of "Paul: Apostle of Christ," which took in $5 million this weekend for Sony's Affirm Films.

And in limited release, Wes Anderson's stop-motion animated "Isle of Dogs" got off to a healthy start, with $1.6 million in 27 theaters. Fox Searchlight, coming off its best picture win at the Academy Awards for "The Shape of Water," carefully selected the opening weekend theaters to cater to Anderson's diehard fans.

"We just wanted to be out there to give his audience an opportunity to find the film," said Frank Rodriguez, head of distribution for Searchlight.

Estimated ticket sales for Friday through Sunday at U.S. and Canadian theaters, according to comScore. Where available, the latest international numbers also are included. Final three-day domestic figures will be released Monday.