With totals expected to top more than $110m (£65m) over the Memorial Day weekend, the film has left last week’s number one movie in its wake.
Brit director Gareth Edwards’ monster movie earned $31.4m (£18.6m) bringing its total US tally to $149m (£88.4m) since its release.
Blended, starring Adam Sandler and Drew Barrymore, took the third spot.
The rom-com, which sees Sandler and Barrymore reunite on the big screen for a third time, took a disappointing $14.2m (£8.4m).
Seth Rogen and Zac Efron comedy Neighbors took $14m (£8.3m), taking it over the $100m (£59.3m) in the US while The Amazing Spider-Man 2 rounded out the top five with $8m (£4.7m)in its fourth weekend on release.
Fears that a series of sexual assault claims filed against X-Men director Bryan Singer would harm the film’s box office proved to be unfounded as its takings gave it the fifth biggest Memorial Day weekend.
The filmmaker, who denies the charges, even dropped out of doing any press interviews for the film.
Paul Dergarabedian, senior media analyst for box-office tracker Rentrak, said: “Rarely do outside situations impact the box office.
“The true fans, all they care about is the movie.”
The film, a time-travelling sequel to the 2011 reboot of the X-Men franchise sees Wolverine, played by Hugh Jackman, being sent from a dystopian future back to 1973 to save the future of mutantkind.