A sci-fi love story has given way to an earthbound romance at the weekend box office.

"Dear John" debuted as the No. 1 movie with $32.4 million, knocking off the blockbuster "Avatar" after seven weekends in first place.

Adapted from Nicholas Sparks' novel, "Dear John" stars Channing Tatum and Amanda Seyfried in a long-distance love story between a soldier and his sweetheart back home.

"Avatar" slipped to No. 2 with $23.6 million, raising its domestic total to $630.1 million. Directed by James Cameron, "Avatar" surpassed his own "Titanic," which had held the domestic revenue record at $600.8 million.

With a record $2.2 billion worldwide, "Avatar" also soared past the $1.8 billion "Titanic" took in globally.