|Liam Neeson has proven himself a known quantity again at the box office.
Neeson's thriller, Unknown, debuted as the No. 1 movie with $21.8 million, following in the footsteps of his 2009 action hit Taken, according to studio estimates on Sunday.
Another action tale, I Am Number Four, opened at No. 2 with $19.5 million.
A Warner Bros. release, Unknown stars Neeson as a botanist who awakens from a coma to find his wife claims she does not know him and that another man has taken his identity.
DreamWorks' I Am Number Four stars Alex Pettyfer as a teenage alien refugee on Earth who develops superpowers to battle the evil invaders that destroyed his planet.
It was the first DreamWorks movie released under the company's distribution deal with Disney.
Disney's animated comedy, Gnomeo & Juliet, was No. 3 with $19.4 million.
Adam Sandler and Jennifer Aniston's romance Just Go With It, which had been No. 1 the previous weekend, fell to fourth place with $18.2 million. The Sony release lifted its total to $60.8 million.
The weekend's other new wide release, Martin Lawrence's comedy, Big Mommas: Like Father, Like Son, was No. 5 with $17 million.
The 20th Century Fox sequel has Lawrence reprising his role as a federal agent who goes undercover as a hefty woman to crack a case.