Rachel McAdams had everyone choked up at the Oscars. There wasn't a dry eye in the house after she honored her late friend Diane Keaton in the award show's In Memoriam segment.

Rachel told the audience, "Believe me when I say there isn't an actress of my generation who is not inspired by and enthralled with her absolute singularity."

She added ... “She wore so many hats, literally and figuratively, actress, artist, author, activist, but no hat more important to her than being a mother to her two children. She meant so much to so many of us. I remember she used to sing this old Girl Scout song she used to sing on set, which is just so her: ‘Make new friends, but keep the old. One is silver, and the other is gold. A circle is round, it has no end. That’s how long I’ll be your friend.’ And so to our friend, Diane Keaton, celebrating a life in silver and gold, a legend with no end."

Remember ... Rachel starred alongside Diane in the 2005 rom-com "The Family Stone."

Diane -- a 4-time Academy Award nominee -- passed away from pneumonia on October 11. She was 79.