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Scarlett Johansson has come out on top in a box office tussle with former wrestler Dwayne "The Rock" Johnson.

Johansson's Lucy, an action thriller about a woman who unlocks hitherto untapped brain powers, made $44m (£26m) in the US and Canada over the weekend, according to studio estimates.

Johnson's fantasy Hercules had to settle for an estimated $29m (£17m) between Friday and Sunday.

The film's distributor Paramount said the takings equalled expectations.

"It's exactly what we had hoped for," said Megan Colligan, head of domestic marketing and distribution at Paramount Pictures.

Directed by France's Luc Besson, Lucy tells of a woman who can move objects with her mind after a drug causes her brain to operate at abnormally high levels.

Hercules sees Johnson take on the role of the fabled Greek demigod, previously played on screen by Steve Reeves, Arnold Schwarzenegger and others.

Brett Ratner's film performed far more strongly than The Legend of Hercules, another outing for the character that could only muster $8.6m (£5m) when it opened in US cinemas in January.

Overall North American box office takings are still down around 20% compared to last year's record summer.

It is hoped Guardians of the Galaxy, the latest comic book fantasy from the Marvel stable, will reverse the trend when it opens in cinemas later this week.

Dawn of the Planet of the Apes, last week's box office champ, fell two places to three with third weekend takings of $16.4m (£9.6m).

That was enough to rank it above thriller sequel The Purge: Anarchy and Disney's Planes: Fire and Rescue, both of which were also down two places on last week's placings.

Two other new entries enjoyed more limited success than Lucy and Hercules, with both making their debuts outside of this week's top five.

And So It Goes, a romantic comedy starring Michael Douglas and Diane Keaton, opened at eight with first weekend takings of $4.6m (£2.7m), while A Most Wanted Man made its bow at 10 with a $2.7m (£1.6m) tally.

Based on a novel by John Le Carre, the espionage thriller - released in the UK in September - stars the late Philip Seymour Hoffman as an anti-terrorist chief stationed in Hamburg.