Newly minted action hero Liam Neeson topped the weekend box office with Unknown.

The movie earned $21.8 million in its first three days of release. Neeson also had a big hit with the action-packed Taken in 2009 -- read on after the jump.

* The teenage alien flick I Am Number Four was number-two with $19.5 million.

* The weekend's other new release, Big Mommas: Like Father, Like Son, landed in fifth with $17 million.

* Gnomeo and Juliet remained in third with $19.4 million.

* And the Adam Sandler -- Jennifer Aniston Just Go With It tumbled all the way from first to fourth with $18.2 million.