Sitting in the audience at the Geffen Playhouse in Los Angeles on Wednesday night, Paltrow, 41, watched Danner, 71, a Tony award-winning actress, perform in The Country House, and was moved by one of the play's more dramatic moments.
"She was tearing up at a scene where her mother – who plays a legendary actress – has a confrontation with her grown-up, depressed son," a theatergoer tells PEOPLE. "It was sweet to see her watching her mom."
Joining Paltrow for the night out was close friend Gavin Rossdale, who was spotted waiting in the Geffen lobby before she arrived. The pals then chatted in their seats.
"She was talking about how it was the perfect part for her mom, and proudly told Gavin about her mom's theater history," says the onlooker.
The Chekhov-inspired play, which costars Scandal's Scott Foley, is headed to Broadway this fall.