Audiences tied the knot with the romantic comedy “No Strings Attached,” driving it to the No. 1 spot at the box office on its opening weekend.

The Paramount Pictures film, starring Ashton Kutcher and Natalie Portman as sex buddies, earned an estimated $20.3 million, according to studio estimates released yesterday.

Last week’s No. 1 movie, “The Green Hornet,” dropped to second place with $18.1 million. It has now made $63.4 million total. “The Dilemma” collected $9.7 million to grab the third spot on the list.