NEW YORK, June 10 (Reuters) - For more than half a century, Chris Evert and Martina Navratilova have stood as twin pillars of modern sport - rivals, friends, foils and co-authors of one of tennis's most compelling stories.

Their duels shaped an era, transcended the game and helped redefine what female athletes could be: fierce, vulnerable, political, glamorous and unapologetically themselves.

Now, more than 50 years after first meeting as teenagers, the two women whose lives became forever intertwined sit together in New York ahead of the premiere of their Netflix ( NFLX ) documentary "Chris and Martina: The Final Set" to reflect not only on a rivalry for the ages, but on a friendship that endured long after the final point was played.

"It's mind-blowing actually, when you think about the first time we met each other," Navratilova, who turns 70 later this year, said, casting her mind back a lifetime ago. "I remember it better than Chris, because Chris was famous already and I was a nobody.

"If you had told us what would happen it would be 'You're crazy'. And if you'd told us what careers we were going to have, it would be 'No way. There's no way this is happening'," she added, before smiling toward her lifelong adversary and friend.

Evert nodded. "We were so different in our younger years," she said. "I was this good Catholic girl, prim and proper... I have my nail polish and my little earrings, and you know... trying to be feminine at the same time, and Martina was the jock, she was the athlete. We were so different in every way, shape or form.

"But there's something there. I guess the depth of all of our experiences and our emotions and we've been through each other's most important aspects of their life, everything that's happened between sickness and marriages and everything," added the 71-year-old Evert.

"We've always been there for each other... that's the common denominator."

ILLNESS DEEPENS FRIENDSHIP

That common denominator became even more profound during their twin battles with cancer. Evert was diagnosed with ovarian cancer in 2021 and Navratilova with throat and breast cancer two years later -- battles they both overcame, and experiences that transformed an already extraordinary bond into something deeper still.

"Well, Martina was my friend at the time but I think it magnified the fact that she was very loyal and she was very supportive and she would always be there for me. We shared this experience. It's nice to be in the trenches with someone that you really care about," Evert said.

For Navratilova, the ordeal sharpened everything they had spent decades building together.

"It brought us to a different level in the friendship relationship," she said. "Trust, and empathy... we already had a lot but now it is like 'Holy shit, we could both die'.

"It gets really serious, this is not a tennis match. So it just amplified everything," Navratilova continued.

"I know how tough she is. She knows how tough I am... when push comes to shove, we were always okay. We came through it with flying colours," she said, before flashing her nemesis-turned-bestie a grin.