LOS ANGELES – In a startling upset, the Producers Guild of America gave its top prize to “The King’s Speech” Saturday night, handing front-runner “The Social Network” its first loss of the awards season and making the race for the best picture Oscar all the more interesting.

Until the PGA Awards, “The Social Network,” the acclaimed drama about the Harvard undergrad founders of Facebook, seemed unstoppable, winning the majority of critics’ honors as well as the Golden Globe and Critics Choice Movie Award for best film.

By inflicting this chink in the armor of “Social Network,” “King’s Speech,” a moving drama from director Tom Hooper about King George VI’s efforts to conquer his stuttering, is now a serious contender for the Oscar that had seemed all but destined for the edgier David Fincher movie.

The PGA and the Academy of Motion Picture Arts and Sciences have agreed on best picture winners the last three years. There are 446 members in the producers branch of the academy.

The Screen Actors Guild Awards, to be held next week, could also deviate from the “Social Network” track, with a best ensemble in a film nod to “King’s Speech” or possibly David O. Russell’s boxing film, “The Fighter,” which has a number of lauded acting performances.