The latest film in a series that began with Ridley Scott's 1979 blockbuster "Alien" earned an estimated $41.5 million for the Friday-through-Sunday period, industry watcher Exhibitor Relations reported.
That was "an excellent opening for a late-episode horror sequel," said David A. Gross of Franchise Entertainment Research.
Directed by Uruguayan filmmaker Fede Alvarez (of 2013's "Evil Dead"), "Romulus" tells the story of space colonists who, while scavenging in an abandoned space station, encounter a dreaded, face-eating alien.
Cailee Spaeny, David Jonsson, Archie Renaux and Spike Fearn star.
That strong result finally dethroned Marvel's superhero comedy "Deadpool & Wolverine," which slipped to second, taking in $29 million in its fourth weekend out. Ryan Reynolds plays Deadpool with Hugh Jackman reprising his role as Wolverine.
That pushed last weekend's number two -- Sony's dramatic romance "It Ends With Us," based on the Colleen Hoover novel -- down to third, with a still-impressive $24 million.
Behind actor and producer Blake Lively, the film scored one of the best-ever openings for a romance film, despite a very public spat between Lively and co-star and director Justin Baldoni.
In fourth was Universal and Amblin Entertainment's weather thriller "Twisters," at $9.8 million. Daisy Edgar-Jones and Glen Powell star in the standalone sequel to the 1996 classic disaster film.
And in fifth was the 15th anniversary re-release of stop-motion classic "Coraline" from Focus Features, at $8.4 million. Based on the Neil Gaiman novella, "Coraline" tells the story of a lonely 11-year-old who discovers an alternate universe behind a mysterious door.
Analyst Gross said successful summer sequels like "Romulus," "Twisters" and "Deadpool" were "an absolute boon to the industry," employing thousands of artists and craftspeople and giving moviemakers the financial leeway to take bigger risks.
Rounding out the top 10 were:
"Despicable Me 4" ($6 million)
"Trap" ($3.4 million)
"Inside Out 2" ($3.2 million)
"Borderlands" ($2.4 million)
"Stree 2" ($2.3 million)
