'Unknown' is No. 1

LOS ANGELES - Liam Neeson's thriller "Unknown" debuted as the No. 1 movie with $21.8 million, according to studio estimates Sunday.

Neeson plays a botanist who awakens from a coma to find his wife claims she doesn't know him and that another man has taken his identity.

Another action flick, "I Am Number Four," opened at No. 2 with $19.5 million. The film stars Alex Pettyfer as an alien refugee on Earth who develops superpowers to battle the evil invaders that destroyed his planet.

The other new release, Martin Lawrence's comedy "Big Mommas: Like Father, Like Son," was No. 5.

1. "Unknown," $ 21.8 million.

2. "I Am Number Four," $19.5 million.

3. "Gnomeo & Juliet," $19.4 million.

5. "Big Mommas: Like Father Like Son," $17 million.

6. "Justin Bieber: Never Say Never," $13.6 million

7. "The King's Speech," $6.6 million.

8. "The Roommate," $4.1 million.

9. "The Eagle," $3.6 million.