At the San Diego world premiere of the new Broadway-bound musical based on Cameron Crowe’s “Almost Famous,” the house was packed with rock writers, and Joni Mitchell was there.

In the show, lead actors Casey Likes and Solea Pfeiffer sing “River,” one of Mitchell’s most enduring hits.

The show features an original score by Tom Kitt, who co-wrote lyrics with Crowe, in addition to some beloved classics like “Tiny Dancer.”

Post-performance at the Old Globe at an outdoor party, Mitchell “proved she can still party like a rock star” an attendee said, by closing the bash down after 1 a.m. alongside the cast.

We’re told that special arrangements had to be made for Likes, who’s just 17, to be admitted into the party, after he was turned away from a first preview bar bash a few weeks ago.

Also spotted at the opening was Pennie Lane Trumbull, the real-life inspiration for the “Band Aid” character that Pfeiffer plays onstage and Kate Hudson originated in the film.

The musical is set in San Diego, where Crowe grew up.