A third straight day of marathon negotiations between Hollywood studios and striking screenwriters ended on Friday night without a deal. But the sides made substantial progress, according to three people briefed on the talks.

The sides reconvened on Saturday.

The Friday session started at 11 a.m. Pacific time at the suburban Los Angeles headquarters of the Alliance of Motion Picture and Television Producers, which bargains on behalf of the major entertainment companies. For the third day in a row, several Hollywood moguls directly participated in the negotiations, which ended a little after 8 p.m.

Robert A. Iger, Disney’s chief executive; Donna Langley, NBCUniversal’s chief content officer of Universal Pictures; Ted Sarandos, co-chief executive of Netflix; and David Zaslav, the chief executive of Warner Bros. Discovery had previously delegated bargaining with the union to others. Their direct involvement — which many screenwriters and some analysts said was long overdue —…