The World Team Tennis Finals are Friday at the West Side Tennis Club in Forest Hills, the site of two of Billie Jean King’s lasting achievements: four U.S. Open singles titles and WTT, which she co-founded in 1974.

WTT embodies King’s life philosophy.

“It’s equality,” said King, 72. “It’s helping each other.”

New York’s WTT franchise, the newly named Empire, relocated to Forest Hills this year and is coached by Patrick McEnroe.

“They’ve been absolutely screaming and yelling for the team,” King said of Empire fans. “I love it.”

Team Tennis pits two squads playing men’s and women’s singles, doubles and mixed doubles. It features fan-friendly rules, encouraging spectator participation. King and partner Ilana Kloss, WTT’s commissioner, live in New York City doing the league’s year-round grass-roots work. WTT has provided 350,000 starter rackets to kids.

Returning to the U.S. Open’s former home, King forgot how much nicer the men’s locker rooms are than the women’s.

“I was like, ‘What? No wonder they never came out of this place!’ ” she said, laughing.

The San Diego Aviators and Orange County Breakers meet Friday at the club where King debuted in 1959, blowing a first-round match point to Justina Bricka.

“You get that close, you’ve got to finish,” said the famously competitive King.

In 1973, King founded the Women’s Tennis Association (WTA), and threatened to boycott her U.S. Open title defense if women’s prize money didn’t equal men’s. It worked.

One of pro sports’ first openly gay celebrities, King remains an activist for social equality, which she calls inclusion.

“I’m pleased with where we are,” King said of the LGBT movement, saying of social media, “I think it’s made all the difference in the world.”

King actively campaigns for close friend Hillary Clinton. She compares the Clinton-Donald Trump presidential race to her 1973 “Battle of the Sexes” win over Bobby Riggs.

Did King think she’d see gay athletes accepted, female athletes making tens of millions or a female presidential candidate?

“That was my prayer,” she said. “But I didn’t know if I’d make it, if I’d still be alive.”

The U.S. Open starts Monday at the Billie Jean King National Tennis Center in Flushing Meadows. Being called “the most influential female athlete ever” shocks and honors King, she says, but isn’t her focus.

“I think of responsibility, and that I have to keep going until my last breath,” she said.