When Peaches Bartkowicz and Chris Evert put their left hands above their right hands to grip their tennis racquets, they were girls in grade school unknowingly defying tennis orthodoxy to hit backhands the way that felt most comfortable. Today, more than half a century later, a little girl who hit backhands without using both hands would be the one defying tennis orthodoxy. One-handed backhands have almost completely disappeared from women’s tennis. And that’s thanks in part to the success that Bartkowicz and Evert had with their two-handed backhands.

In the latest installment in our documentary podcast series Ahead Of Their Time, we look at Bartkowicz and Evert, the innovators who brought the two-handed backhand to women’s tennis in a major way. Evert’s story is well-known: She rode her backhand, accuracy and focus to 18 Grand Slam singles titles. Bartkowicz’s is more obscure: After an extraordinary juniors career, she never reached a Grand Slam semifinal as a pro and played her last Slam soon after turning 22.

But Bartkowicz’s backhand was ahead of her time. When she was just 12, a photo of her swinging with two hands at the Southern Girls Tennis Tournament appeared in the Louisville Courier-Journal. The caption began with the all-caps “TWO HANDS!” and called the shot a “baseball backhand.” When she won the 1965 U.S. Open girls title, The New York Times commended her “tremendous marksmanship” with that shot. By the time she closed out her junior career without a loss at the 1967 U.S. Open, the Philadelphia Inquirer called her “the foremost exponent of the two-handed backhand in women’s competition.”

Evert is nearly six years younger than Bartkowicz and was unknown when Bartkowicz’s baseball backhand became famous. But Evert soon surpassed her older rival. She played her first Grand Slam at the 1971 U.S. Open — just two months after Bartkowicz played her last major at Wimbledon — and made the semifinals at age 16. In 1974, Evert won her first two Grand Slam titles, and the first two on record by a woman who hits a two-handed backhand. (A few notable men used two-handed backhands in the 1930s and 1940s, but the shot had mostly fallen back out of favor among men, too, when Bartkowicz and Evert were starting out.) By the time Evert won her last major, in 1986, her signature shot was tightening its grip in the sport, thanks also to its use by men’s champions Jimmy Connors and Bjorn Borg. And two years after Evert’s retirement, Monica Seles won three of four majors while using two hands on both backhands and forehands.

By 2014, when The Economist tracked the decline of one-handed backhands in the pro game, just one woman with a one-handed backhand had won a major since 2008: Francesca Schiavone, at the 2010 French Open.

The two-handed backhand’s dominance has continued: Its users have won 35 of the last 36 women’s major titles. Every woman in the top 10 and 48 of the top 50 use it. It’s also become the dominant backhand in men’s tennis, though with accomplished one-handed holdouts such as Roger Federer, Stan Wawrinka and Dominic Thiem. (Tennis-nerd note: Every player occasionally hits backhands with one hand, especially in defensive positions, either to slice the ball or when forced to take a hand off the racquet to reach the ball. What we’re talking about are how players hit the backhand when they have time to get to the ball and drive it offensively.)

Bartkowicz and Evert hit their backhands with two hands because they felt just one didn’t give them enough strength. The two-hander took over pro tennis for similar reasons. Using their off hand on backhands lets players hit with additional power, which gives the ball more speed and spin, especially in concert with the latest racquet and string technology. The one-hander’s advantages — better feel for the ball, more equipped for wide reaches and low bounces, smoother transition to one-handed backhand volleys at net — count less in a game played rarely on low-bouncing, volley-friendly grass and usually contested behind the baseline.

The two-handed backhand is especially valuable when returning serves, as the extra support helps to absorb and redirect powerful, high-bouncing shots. Tennis analyst Jeff Sackmann has shown that in men’s pro tennis, players with two-handed backhands get the return in play more often, and win the point more often when they do. Data collected through Sackmann’s crowdsourced Match Charting Project for the women’s game shows the same general trends: Players with two-handed backhands have more success returning serves than do players with one-handed backhands. It’s hard to reach firm conclusions because there are simply so few women hitting one-handed backhands.

The dearth of top women using one-handed backhands may be the most compelling data point demonstrating the two-handed backhand’s dominance: If it weren’t the best option, more women would be hitting backhands with one hand. Tennis, like all sports, has its share of domineering coaches, but it is also primarily an individual and individualistic sport. Players command their own games and choose the shots and tactics that will win the most. That makes tennis a sport that breeds innovation, whether it’s among pros at a Slam or among two young girls who chose the backhand that best suited them. And if the one-handed backhand ever makes a comeback in women’s tennis, it might begin with a girl defying orthodoxy and taking one hand off the racquet.

Emma Morgenstern contributed research.

This is part of our new podcast series “Ahead Of Their Time,” profiling players and managers in various sports who were underappreciated in their era.