Battle of the Sexes directors Valerie Faris and Jonathan Dayton said they saw a "similar spirit" in Emma Stone and Billie Jean King, who the Oscar winning actress plays in the film.
The film tells the story of the 1973 tennis match between Billie Jean King and Bobby Riggs, who are played by Stone and Steve Carell.
Speaking to RTÉ Entertainment about Stone's casting as the tennis great, Faris said, "I think just knowing Emma and seeing how much she wanted this and how much respect she had for Billie Jean, and how scared she was by it – we knew she was just going to put everything into it. And also knowing who Emma is, there's a similar spirit they have."
Dayton added that they met Stone years before King, and instantly saw similarities between the pair. "There's something in them, this energy, this life, this hunger..." Dayton said.
With the film coming decades after the sporting event took place, Faris said that the time was only right now to make it as Stone and Carell were old enough for the roles.
"Because Emma and Steve weren't the right age yet, we were waiting for them to get there," Faris laughed.
Dayton said seeing the film had a big affect on King as it had been so long since she had watched the match, and it was a "painful time" for her.
"It kind of blew her mind to see all this. She hadn't watched the match in 25 years, it was a painful time for her, and it was obviously a moment where she made great advances," he said.
Battle of the Sexes is in cinemas now.