She beat out Jane Fonda in Julia, Anne Bancroft and Shirley MacLaine in The Turning Point and Marsha Mason in The Goodbye Girl.
shareOne can easily come up with a better 5:
Isabelle Huppert - The Lacemaker
Sissy Spacek and Shelley Duvall - 3 Women
Liza Minnelli - New York, New York
Diane Keaton - Annie Hall or Looking for Mr. Goodbar
Diane Keaton at the time was a female archetype, plus she was with Woody Allen, and pretty cute, and not to forget Annie Hall was a great role ... penned by Woody Allen and Marshall Brickman. The movie was incredibly innovative, like the moments when Woody turns to the camera and breaks the Fourth Wall, I think it's called. All of that must have been a big factor in the movie's awards.
We forget it at the time, but Woody Allen was hot, very creative and innovative, and profitable for his investors. His movies were a big deal. Then Diane got all political, but she is still in some good movies occasionally.
In 1977, Diane Keaton not only starred in Annie Hall, she starred in Looking for Mr. Goodbar, based on the true story of a teacher by day who by night cruised bars picking men up for sex. Keaton did sex scenes and nudity in that rough drama.
It was rumored that Keaton won both for Annie Hall and Looking for Mr. Goodbar.
Also in 1977, Richard Dreyfuss appeared in both The Goodbye Girl and Close Encounters. He won for Goodbye Girl, but maybe both.