NEW YORK - Serena Williams' US Open adventure is over, capping a glittering 27-year career that defined a new era of tennis and inspired sponsors to take female athletes more seriously.

Williams lost to Australia's Ajla Tomljanovic in three sets at Arthur Ashe Stadium in New York Friday, a day after she and her sister Venus exited the doubles competition after a first-round loss.

Williams is expected to retire after completing play in the tournament.

The Williams sisters helped usher in a new era of sponsorships for female athletes over their decorated careers.

Mr Jeff Kearney, global head of sports marketing for Gatorade, said Serena has made a permanent impact on marketing budgets everywhere, and her overwhelming success convinced the Pepsico division, which first partnered with Williams in 2009, to spend more on female athletes.

"Across brands and the different companies she works with, they're investing more on the women's game," said Mr Kearney.

'She's going to transcend sport'

The sports icon has worked with a number of brands, beginning with a five-year Puma sponsorship at the beginning of her career that was valued at US$13 million (S$18 million).

A longstanding partnership with Nike followed in 2003, which has grown to include an in-house incubator for fashion designers. (The company has also dedicated the largest building on its Beaverton, Oregon, campus to her.) Delta Air Lines and JPMorgan Chase & Co have also been sponsors.

"The thing about Serena is she's going to transcend sport," said Ms Tanya Hvizdak, vice-president of global women's sports marketing at Nike.

"She's been able to show it's beyond performance. Obviously that's provided her a platform, but her engagement in so many different other aspects and showing the dimensions of herself, whether it's as a mother or a champion of diverse designers or other aspects, will be her legacy," said Ms Hvizdak.

Fighting for what they're worth

Female athletes have long had to fight for what they're worth, from sponsorships or institutional pay.

The US Soccer Federation announced only this year that male and female athletes would be compensated equally, and pay disparities persist for female golf, basketball and tennis players.

For its part, Nike changed its pay policies for pregnant athletes after runner Allyson Felix and others alleged that they were mistreated during their pregnancies.

In March, the company also unveiled a new think-tank initiative, which includes Williams and 12 other Nike-sponsored female athletes.

Now, as Williams prepares for what she called the "evolution" of her career in a recent Vogue essay announcing her retirement - with hopes to one day run a billion-dollar venture capital fund - she has proof that she can level up and a track record of inspiring brands to give female athletes their due.

"I'd like to think that thanks to opportunities afforded to me, women athletes feel that they can be themselves on the court," she said in Vogue.

'She's a catalyst'

Anheuser-Busch InBev's Michelob Ultra beer brand, another major sports sponsor, has worked with Williams in the late stages of her career, with Super Bowl ads such as one alongside WNBA star Nneka Ogwumike and Women's World Cup champion Alex Morgan.

Mr Ricardo Marques, vice-president of marketing, said Williams played a pivotal role in boosting dollars spent on women in sports.

Last year, Michelob committed US$100 million to marketing women's sports over five years, pledging equal representation of females and males on its endorsement roster.

Executives said half of its lifestyle content will promote women athletes by 2025.

"Serena was a catalyst," said Mr Marques. "She gave confidence to brands like us to come forward and put these commitments, dollars, to make that support more visible."

That support includes standing by Williams and other athletes as they navigate inequities baked into tennis.

Money's coming into play

The Williams sisters were both made to endure racism throughout their careers, and Serena is no stranger to calling out double standards and unfair treatment. Her sponsors have followed suit.

After the French Open objected to a jumpsuit she wore to the 2018 tournament, Nike tweeted its support.

"Support in those moments is key because not only does it raise an element of yes, that was in the arena of sport and us supporting that athlete, but even more so, women's rights and opportunities in that aspect," said Ms Hvizdak.

That the jumpsuit supported Williams in both design and functionality - it provided compression to help with blood clots - underscored Nike's commitment to work with Williams and other female athletes with regard to what they individually need, she added.

As viewership and support continues to grow for women's sports, brands are prepared to continue investing in female athletes and leagues.

"You're seeing the money come into play, but there needs to be more of it industry wide," said Ms Hvizdak.

"We continue to lead in this space and we need to pull people with us. That's the goal," she said.

And although Williams may soon be bidding the tournament circuit farewell, brands aren't moving on from working with her if she'll have them.

"Her name is always at the top of the list," said Gatorade's Mr Kearney. BLOOMBERG