When Serena Williams steps onto the court for her U.S. Open semifinal on Friday, she will be just two wins away from further etching her mark in tennis history. For the 32-year-old, a victory over Ekaterina Makarova backed up by triumph in the final on Sunday would see her join two of the iconic names of tennis, Chris Evert and Martina Navratilova, on 18 Grand Slam singles titles, second only to Steffi Graf’s 22 in the Open era. It would also put her level with Evert for the most U.S. Open titles in the Open era with six.

Those records will surely enter her head when she battles it out on Arthur Ashe Stadium, but Williams could be forgiven for also allowing another historic achievement to come into her thinking. Should Williams lift the trophy, she would also walk home with the biggest paycheck ever for a single tennis tournament of $4 million.

The prize money at tennis grand slams has increased rapidly in recent years, particularly after players demanded a bigger share of the revenue pie. This year the Australian Open singles’ champions were rewarded with 2.65 million Australian dollars ($2.49 million), while their French Open counterparts secured 1.65 million Euros ($2.14 million) and the winners at Wimbledon were rewarded with 1.76 million pounds ($2.87 million). Trumping its counterparts, though, $3 million will be awarded to both men’s and women’s champions at the U.S. Open. And if the winner is Williams, her prize money will be boosted considerably by having won the U.S. Open Series. Designed to add interest to the tournaments that take place in North America in the run up to the year’s final Grand Slam, the Emirates-Airline-sponsored U.S. Open series presents the winner with the chance to increase their paycheck by $1 million should they go onto win the U.S. Open.

That is the prize that now awaits Williams, who already holds the previous record of $3.6 million jointly with Rafael Nadal for completing the same feat last year. As the world No. 1, and having seen all of the top nine seeds already fall by the wayside in what has been a wildly unpredictable women’s event at Flushing Meadows, it is a prize she is expected to collect. But then most will have anticipated that Grand Slam 18 will already have been in her possession. Instead, despite dominating the tour for the previous 18 months, she has struggled this year, falling before the quarterfinal stage at the Australian Open, French Open and Wimbledon.

Now, on home soil, and with the added lure of a record financial reward, the pressure is more intense than ever. Not that Williams will be short of cash anytime soon were she to fall in either Friday’s semifinal or in Sunday’s final, where either a rejuvenated Caroline Wozniacki or China’s Peng Shuai will await. Williams already leads the way by some distance on the all-time prize money list on the Women’s Tennis Association (WTA) tour. With $56.9 million banked coming into the U.S. Open, she has made almost double the amount of her nearest challenger on the list, Maria Sharapova, who has garnered a far from shabby $30.1 million.

Despite being at an age that was once considered retirement time for female tennis players, last year was Williams’s most dominant yet, reflected by her smashing the previous season record for earnings on the WTA Tour with $12.4 million. Next on the list was Belarussian Victoria Azarenka at $6.5 million. The startling sums of money are a testament to tennis being the one major sport where women have achieved equality when it comes to prize money and near-equality in profile. Seven of the top 10 highest-paid female athletes between June 2013 and June 2014 were tennis players, according to Forbes. Were Williams to claim the historic sum of prize money on Sunday, it would be in fitting surroundings. In 1973, a momentous year for women in the sport which also saw key figure Billie Jean King defeat Bobby Riggs in the Battle of the Sexes and the forming of the WTA tour, the U.S. Open became the first Grand Slam to offer equal prize money for men and women.

While there is now established, although still debated by some, equality in the sport, there exists, as with the men, a great disparity between the top women and the rest. Williams’s opponent on Friday, Makarova, finished 2013 ranked 24th in the world but made the comparatively small sum of $944,618 from singles action. In comparison to Williams’s possible payout of $4 million in Flushing Meadows, young American Taylor Townsend, whom she ousted in the first round, pocketed under $36,000. That figure roughly doubles up all the way through the rounds, with the runner up taking home $1.45 million.

It is a sharp drop off to the losers in the early rounds then, despite the players having banded together recently to campaign for those not taking home the biggest prizes on a weekly basis to be better rewarded. For many trying to break into the sport’s elite it can be tough. Men’s tour player Dmitry Tursunov, currently ranked No. 57, but who has been as high as 20, estimated to CNN that he needed to make $200,000 a year just to break even, giving the considerable traveling expenses not just for himself but a coach, too. On the women’s tour, it is a figure that not many ranked outside of the world’s top 100 will be able to make.

For the top players, though, prize money for their athletic achievements is far from the sum total of their earnings. For the period between June last year and this year, Williams’ $11 million in prize money was matched by the same amount in endorsements from deals with the likes of Nike and Wilson. Yet, for all her dominance in the best rewarded women’s sport, Williams is surprisingly not the best-paid female athlete. Indeed, she falls behind two rivals whom she dwarfed in on-court earnings last year. The $18 million in endorsements reaped by Li Na over the same period illustrates the huge money to be made in the Chinese and Asian market. Li, the first ever Asian-born player to win a Grand Slam, claimed her second major when triumphing at the Australian Open earlier this year. Still, neither Li nor Williams can touch Maria Sharapova when it comes to off-court revenue -- an illustration surely that glamor still counts for much. She may have beaten Sharapova on 15 straight occasions on the court, but Williams’s endorsement earnings are just half that of Sharapova’s monstrous $22 million.  

That is unlikely to change anytime soon, but if Williams lifts the U.S. Open trophy on Sunday she will again secure her position as the undisputed queen on the court and, for her efforts, be more richly rewarded that any player in history.