They were world-class tennis rivals. Now friends, they've teamed up against cancer

Once rivals on the tennis court, Martina Navratilova, left, and Chris Evert have become close friends in retirement. They are pictured above at the French Open in 1986. Trevor Jones/Getty Images Europe hide caption toggle caption Trevor Jones/Getty Images Europe Chris Evert and Martina Navratilova were the most successful women's tennis champions of their generation. Both were 18-time Grand Slam tournament winners — and each other's greatest rivals. Evert, a Florida native, became a tennis star in her teens. Navratilova was born in communist Czechoslovakia, and emerged as a player after Evert was established. They first faced off during a match in Akron, Ohio, in 1973, when Evert was 18, and Navratilova was 16. Evert won, but Navratilova left an impression. "I remember thinking to myself, holy cow, when this young girl gets into better shape, she is going to be a force to be reckoned with," Evert says. "She had so much talent. Her hands were quick, she had a big first serve, she had a big forehand, and she just was so powerful." Two years later, on the day she lost a semifinals match to Evert at the U.S. Open, Navratilova defected to the U.S. In the years that followed, her tennis game improved. Though she and Evert had initially been friendly, the friendship cooled as their rivalry heated up. "Playing Chris was difficult because how can you not like Chris? What's not to admire?" Navratilova says. …