Once rivals -- among the most competitive and compelling matchups in the history of sport -- lately they’ve been working side by side for a higher cause.

Several weeks ago in Houston, Martina Navratilova and Chris Evert launched a series of promotional efforts devoted to drawing critical attention to Breast Cancer Awareness Month. They visited the laboratories at The University of Texas MD Anderson Cancer Center and presented a significant grant from the WTA ACEing Cancer by Hologic campaign to gifted researcher Dr. Rachel Dittmar for her project Triple Negative Breast Cancer, a particularly virulent strain.

More recently, the champions of the WTA Foundation’s ACEing Cancer by Hologic campaign shot a video in Fort Lauderdale.

Here’s a snippet:

Chris: Every ace raises money in the fight against cancer.

Martina: A cause that’s close to my heart -- and yours.

Chris: We’ve been in many on-court battles. Like when I beat you in the WTA Finals in ‘75.

Martina: Or when I beat you in ’83 and ’84.

Chris: But now we’re teaming up to battle together.

Martina: Help us ace cancer and go to WTA.com/aceingcancer to learn more.

They were born two years apart, in vastly different circumstances, but Navratilova and Evert have a rich history going back to January 1973 when they first met at the Racquet club of Fort Lauderdale. Evert was playing backgammon and said hello to the shy 16-year-old from Czechoslovakia.

That was 51 years -- more than half a century. They first played a few months later in Akron, Ohio.

They met 80 times over a span of 16 years -- 60 of those were finals -- and the final head-to-head went to Navratilova, 43-37. For nearly 12 years after the WTA Tour rankings were introduced in 1975, one of them held the No.1 ranking for all but 23 weeks. Navratilova won 167 titles, while Evert won 157. Steffi Graf (107) is a distant third on the all-time list.

Perhaps appropriately, they both collected 18 Grand Slam singles titles. With the WTA Finals underway in Riyadh, Saudi Arabia, it might be fitting to note that Navratilova won a record eight titles at the year-end tournament, including six straight from 1981-86. She appeared in 14 finals; Evert is next, with eight.

After five separate bouts with cancer (three for Navratilova, two for Evert), they have a powerful common bond: empathy. When they were at their lowest, a call or a text drastically changed the temperature.

“I think because of what we went through in tennis, we knew what the other one was going through, the losses and the wins,” Navratilova said from her home in South Florida. “We always had a deep empathy for each other because we knew what it took.

“And then the same thing happened with cancer. We just kind of felt each other. We were always aware of each other’s lives, and this brought it to another level in that we kind of knew intuitively what to do, what not to do, supporting each other.”

And that support has helped deliver Navratilova to a busy, fulfilling life that just got busier. She and Julia Lemigova, who have been married for nearly 10 years, recently adopted two boys, now 3 and 2 years old.

“Physically and practically speaking,” Navratilova said, “I don’t know how people do it that don’t have help. It is just so exhausting. But because of the help I can do the fun things.”

Navratilova survived a 2010 diagnosis of breast cancer and the “double whammy” of the return of breast cancer as well as throat cancer in 2023.

The treatments in New York City, Navratilova remembered, were exhausting.

“Outside of going to the grocery store or picking up some stuff, I went for one walk outside in seven weeks,” she said. “I couldn’t get out of bed. I had my yoga mat, and I spent half an hour, total, on it, stretching. I couldn’t even do the downward dog position.”

Evert learned she had stage 1 ovarian cancer late in 2021, which killed her younger sister, also a tennis pro, four years ago. Evert beat that only for it to reoccur a little more than a year later after she was in remission. Now, after a rigorous course of action, she says she’s again cancer-free.

The key, Evert insists, was early testing. After being diagnosed she’s been advocating for genetic testing and says that five women she knows have undergone surgery.

According to Navratilova, they’ve both used their on-court champion’s mentality to aggressively approach cancer.

“You just get on with it,” Navratilova said. “You have a long-term goal, which is to get rid of it. The short-term goal is what do I need to do today? You have the goal, but you may not get there. At least you’re in control [with tennis]. With cancer, you’re not in control.”

A positive approach makes all the difference.

“Studies show you need to surround yourself with positive friends, three to five, who will be there for you, no matter what,” Navratilova said. “When you’re negative, you stress yourself. Stress causes cancer, as well as many other ailments. Having that group of friends was essential for me. And so I knew what to do the second time.”

The message Navratilova and Evert are trying to send is simple: Pay attention. If you feel a lump under your armpit or in your breast, get it checked out. Get a yearly checkup. If you can get the tests for genes that can cause cancer, do it.

“Cervical cancer and breast cancer -- if you don’t catch it early, quite often it’s too late,” Navratilova said. “But if you’re aware, you can catch it early. So, don’t put it off. If something doesn’t feel right, the sooner you nip it in the bud, the better the outcome.”

To learn more about the ACEing Cancer initiative including how to make a donation, visit wtatennis.com/aceingcancer.

To learn more about the WTA Foundation, visit wta.foundation.