"I'm thinking ‘Oh my gosh. It's Lady Gaga. I love her so much. I don't want to tell her the truth,'" she said. "So, I just gracefully thanked her and bowed my head."
The kicker was when Adams walked into the party.
"So I'm like, ‘There's Isla Fisher.'"
She also had an incident at IKEA where a woman and her two kids asked the actress to sing the song from Adams' 2007 movie Enchanted. Even though she described herself as "tone deaf," Fisher honored her request.
"I sang probably three verses before she just backed away realizing that I was clearly not Amy Adams," she said.
Watch the video to see the hilarious PSA and clear up any confusion between the two actresses.