Thriller “Unknown” topped movie box office charts with $21.8 million in ticket sales during a sluggish weekend over the long Presidents Day holiday.

Sci-fi adventure “I Am Number Four,” landed in the No. 2 spot with $19.5 million.

Animated “Gnomeo & Juliet” rounded out the top three on Sunday, earning $19.4 million.

By Sunday, the weekend’s No. 4 movie was comedy “Just Go With It” starring Adam Sandler and Jennifer Aniston. Its ticket sales dropped 40 percent to $18.2 million from last weekend and now total $60.8 million.

The weekend’s other new major release, Martin Lawrence comedy “Big Mommas: Like Father Like Son” claimed the No. 5 spot with a $17 million debut.