Baby Mama has raced kicking and screaming to the top of the U.s. box office charts, taking $18.3 million during its opening weekend.

The comedy, starring Tina Fey and Amy Poehler as a woman desperate for a baby, and the surrogate she hires, replaced Jet Li and Jackie Chan's martial arts movie The Forgotten Kingdom in the number one spot.

Another new entry, Harold and Kumar Escape from Guantanamo Bay, took $14.5 million and second place, ahead of The Forgotten Kingdom with $11.2 million.

Last week's number two, Forgetting Sarah Marshall, collected $11 million, but slipped from two to four in the chart. Children's adventure Nim's Island rounds out the top five, with takings of $4.5 million.