Stone was also in awe of King, and spoke with ET about how she bulked up to portray the real-life tennis legend.
"For the first three weeks, you hate your life, and I know a lot of people hate exercising. I did," Stone -- who gained 15 pounds of muscle for the role -- confessed. "And then after three weeks when you're like, 'I can lift this? I can do this?' It just becomes addictive. It's just really incredible to feel strong. It feels so good."
Check out more of ET's inclusive interview with the actress: