The introduction of Open Tennis in 1968 meant amateur and professional players could compete transparently on the same stages, but it didn’t do much for the women who played the sport. Indeed, in the first couple of years of this promising new era, prize money disparity between the sexes only grew. Adding insult to injury, there were few opportunities for women to shine on their own terms. Tournaments were combined, but far from equal.

Matters came to a head in the summer of 1970, when Jack Kramer’s prestigious Pacific Southwest event in Los Angeles announced that male competitors would be paid more than eight times as much as the so-called ‘fairer sex’ – even though the women’s field would also be packed with stars.

Enter Gladys Heldman, the business-savvy founder and publisher of World Tennis magazine. Devoted to the sport and a fierce advocate of the women who played it, Heldman met with Billie Jean King, Rosie Casals and Nancy Richey at the US Open and counseled against a boycott of Kramer’s event. Instead, when the powerful former champion and promoter would not budge on prize money, Heldman arranged for the Houston Racquet Club to host a new breed of event for the women. Here, key allies included Dolores Hornberger, president of the club’s Women’s Association and Jim Hight, who was president-elect of the Texas LTA and prepared to stand up to the sport’s bosses.

Read more: The Original 9 in pictures

Riding the winds of societal change (a survey conducted by young players Ceci Martinez and Esme Emanuel at the US Open had indicated a healthy market for women’s tennis among female and male fans) the initial $5,000 purse was to come from ticket sales to women’s groups in the Texan city. Heldman also persuaded her friend Joseph Cullman III, an avid tennis fan and chairman of tobacco giant Philip Morris, to provide an additional $2,500 in return for naming rights for his Virginia Slims brand.

For the groundbreaking tournament, called the Virginia Slims Invitational, Heldman recruited players who signed weeklong $1 contracts with her company. More than just a symbolic act, this technicality protected the athletes from any lawsuit that might be launched by the tennis establishment. They became “contract pros”.

Staring down threats they would be banned from Grand Slams and team competitions and lose their national rankings - the USLTA refused to sanction the Houston tournament, let alone entertain King's suggestion that they back a women's tour - nine women (seven Americans and two Australians) took a bold leap of faith: King, Peaches Bartkowicz, Rosie Casals, Judy Dalton, Julie Heldman, Kerry Melville Reid, Kristy Pigeon, Nancy Richey and Valerie Ziegenfuss.

They became known as the Original 9. 

Original 9 trailblazers Nancy Richey, Billie Jean King and Julie Heldman announce the new Virginia Slims Circuit to media in October 1970 (Getty)

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“I felt a sense of both fear and exhilaration,” recalls King of the day matters came to a head – September 23, 1970. “We knew we were making history and we had such a strong sense of purpose. I just kept thinking about the vision we had for the future of our sport. We wanted to ensure that any girl in the world that was good enough would have a place to go and make a living playing tennis.”

Any anxieties were not unfounded; the rebels did suffer consequences. The two Australians in the group, Dalton and Melville Reid, were forced out of their national championships by their own governing body, for instance. Even commercial sponsors weighed in: Dalton – who would finish runner-up to Casals at Houston – was prevented from using her Slazenger racquet for two years.

Still, so pleased was Cullman with the Houston spectacle that his company’s sponsorship skyrocketed – the ensuing 21-event World Tennis Women’s Pro Tour – the Virginia Slims Circuit – offered a total prize purse of around $336,000 in 1971 as more and more players jumped on board. By the end of the year, King had become the first female athlete to earn more than $100,000 in a single season.

After becoming the first female athlete to earn $100,000 in a single year – 1971 – Billie Jean King received a crown and a congratulatory call from US President Richard Nixon (Getty)

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The early 1970s remained a politically fraught time for the sport, though. Traditional tournaments, including the Grand Slam events, were still classified under a separate International Lawn Tennis Federation (ILTF) grand prix umbrella and the USLTA eventually mounted a rival circuit that relied heavily on the appeal of a young Chris Evert and international headliners such as Margaret Court, Evonne Goolagong and Virginia Wade. In practice, the stars played across the different leagues – but the talent pool was divided.

The PR battle was won, ultimately, by the marketing savvy of Virginia Slims and the promotional efforts of the players, who worked tirelessly on and off court to build their fan base.

Clockwise from top left: Original 9 members Valerie Ziegenfuss, Billie Jean King, Nancy Richey, Peaches Bartkowicz, Kristy Pigeon, Julie Heldman, Rosie Casals, Kerry Melville and Judy Dalton were reunited at the Family Circle Cup in Charleston in 2012 .

Chris Smith

Galvanized by the successes of the Slims circuit – the first Virginia Slims Championships were held at Boca Raton, Florida in 1972, with an unprecedented $100,000 purse – but only too aware progress could not be taken for granted, King called a showdown meeting on the eve of Wimbledon in 1973. There, she made an impassioned case for strength in solidarity and was joined by 63 players who voted for the establishment of a new association – the WTA – to represent their interests. Crucially, the top women would now present a united front.

Two months later, the US Open became the first Grand Slam tournament to offer equal prize money to women and men and just weeks after that, King went on to defeat Bobby Riggs in the famous Battle of the Sexes showdown.

Women’s tennis hasn’t looked back.

“Today’s players are living our vision,” King says. “In 1970, and even a few years after we signed the $1 contract with Gladys, people never believed women’s tennis would be a global sport and that players would be making the money they make today. But it is a reality and I know today’s players will continue our dreams for future generations in tennis and inspire other women’s sports as well.”

Get To Know: Billie Jean King