Mirren lucked out with Spector role
The Queen actress scored a Screen Actors Guild Award for best female actor in a television movie or mini-series for the HBO drama, in which she played lawyer Linda Kenney Baden.
Collecting her male statue trophy, the star said she thought her statue was "sexy" and said she did not feel "saggy" despite her win.
Speaking afterwards, she said: "I so did not expect to win. I was sure Elisabeth (Moss) was going to win. I came in a relaxed state. I had a drink - big mistake."
Addressing her role in the drama about the record producer convicted of murder, Dame Helen said: "Bette Midler was originally going to do it. She had to drop out after shooting one week with Al (Pacino). She had a bad neck so had to drop out. I was on holiday in Italy and got a call to do a film with Al Pacino.
"I had to leave my holiday and the lovely time I was having and go into something quite challenging. I lucked out in my role."
But the veteran star was not the only Brit to win big at the glittering ceremony at the Shrine Auditorium in Los Angeles, Dame Maggie Smith scooped the award for best actress in a TV drama series for her role of Lady Violet Crawley in Downton Abbey - but was not there to collect the gong.
Lupita Nyong'o also scored a statue for female actor in a supporting role for her portrayal of Patsey in Steve McQueen's brutal film 12 Years A Slave.
Speaking after she collected the award, she said she hasn't been phased by the attention focused on her wardrobe.
"I actually don't feel pressure because my first love is acting. I've loved the opportunity to learn about the fashion world but I don't want it to take over from acting."