LOS ANGELES, April 25 (Reuters) – “How to Train Your Dragon” proved a difficult film to slay at the North American box office as it took the top spot in its fifth weekend in theaters, according to studio estimates issued on Sunday.

The animated “Dragon” earned $15 million over the weekend since Friday, dropping just 23 percent since last weekend.

Romantic comedy “The Back-up Plan” made $12.3 million, while action comedy “The Losers” opened slightly short of expectations with $9.6 million.

“We couldn’t be more thrilled to be No. 1 in the fifth week,” said Anne Globe, head of worldwide marketing for DreamWorks Animation SKG Inc (DWA.O), the studio that produced “Dragon.”

“The Back-up Plan,” which is Jennifer Lopez’s first movie appearance since 2006, opened within industry expectations. The singer and actress stars opposite Alex O’Loughlin.

The release from CBS Corp’s (CBS.N) film division was made for $35 million. It ruled the Friday night box office, but later lost the lead to “Dragon” as families streamed into matinee showings of the animated film.

“Date Night,” a romantic comedy from News Corp-owned (NWSA.O) Twentieth Century Fox, remained a solid performer in its third weekend since opening. It made $10.6 million, which was only a 37 percent drop from last week.

CBS Films expects “The Back-up Plan” to follow the pattern set by romantic comedies such as “Date Night” and remain strong in future weekends.

“Romantic comedies have been over-performing this year and in the second and third and fourth week, Jennifer Lopez films tend to over-perform and have great legs, as does Jennifer herself I might add,” said Steven Friedlander, executive vice president, distribution, for CBS Films.

Overall, it was a modest weekend at the box office, with no big budget film openings.

“The Losers,” an ensemble action comedy with Chris Evans, Zoe Saldana, Jeffrey Dean Morgan and Idris Elba, was made on a modest budget of $31 million, said the studio behind the film, Time Warner Inc’s (TWX.N) Warner Bros.

The movie about an armed U.S. special forces team is based on a comic book series, and comes out of the DC Entertainment division of Warner Bros.

“Kick-Ass,” another action comedy which last weekend also opened below expectations, failed to stage a comeback as it ended the weekend with an estimated $9.5 million. That was a drop of 52 percent compared to the previous session.

“Dragon,” which is distributed by Viacom Inc’s (VIAb.N) Paramount Pictures division, narrowly lost the box office race last week to “Kick-Ass.”

DreamWorks expects the film to continue to stay strong for the next two weeks, in advance of the summer movie season. (Reporting by Alex Dobuzinskis: Editing by Vicki Allen)