Coco Gauff and Jessica Pegula were born a decade apart, which does not matter so much when it comes to playing tennis together but definitely creates a barrier when the subject is TikTok.

“We don’t really notice the age difference until certain conversations come up,” Gauff said. “It’s definitely a generation divide.” Joked Pegula: “She keeps me young.”

The 28-year-old Pegula is No. 3 in the singles rankings, the 18-year-old Gauff is No. 4, and the two Americans are making their WTA Finals debuts in both singles and doubles this week.

Jessica Pegula. File picture

No other doubles pairing also has participated in the singles competition at the season-ending tournament since sisters Serena and Venus Williams managed to do that in 2009 (Serena beat Venus in the singles final that year).

Gauff and Pegula briefly paired up in 2021, going 0-2, before really thriving in doubles in 2022, collecting three titles and finishing as the runners-up at the French Open in June. Gauff reached No. 1 in the doubles rankings in August and is currently No. 2, one spot ahead of Pegula.

The comfort level with each other on the court and “irl,” as the kids say — “in real life” for the uninformed — is much better than when Gauff brings social media slang into the discussion.

Particularly if the references come from TikTok, a video-sharing app. “She’ll look at me and say, What?!’ I’m like, You’ve never seen that?’ She’s like, No,’” Gauff explained.

“Then,” she added, “it becomes awkward.”

Until Gauff pulls out her cellphone to demonstrate what she’s talking about, “and then it will make sense,” she said.

Pegula, who beat Maria Sakkari in the final of the Guadalajara Open on October 23, called it “a reward and a confidence boost for me” to be in the fields open to only eight singles players and eight doubles teams.

Gauff is the youngest American to qualify for the WTA Finals since 1994 and thinks the accomplishment “just shows my improvement.”

“I busted onto the scene in a very big way, and a lot of people were having opinions on whether or not I would do well or not,” said Gauff, who made her grand slam debut by reaching Wimbledon’s fourth round at age 15.

They recently became the first two US women in the top four of the singles rankings at the same time since the Williams siblings in 2010.

“We learn from each other ... and that’s always kind of pushing us to get better,” Pegula said.

They are aware of differing in-match personas: Pegula is calmer, Gauff more excitable. And they believe each can benefit from adopting at least a hint of the other’s mindset.

“She has really good energy. A lot of first-pumping, jumping around, her athleticism and the youthfulness about her. She’s very giggly. She laughs a lot. She’s always kind of messing around,” Pegula said.

Ask for Gauff’s take on Pegula, and among the words that arise are serious, chill, humble, kind.

“She’s not on TikTok at all. If you follow her on Instagram, she’s barely on there. I would say Twitter is her most-used platform, and it’s still not used a lot,” Gauff said, chuckling. “So maybe I can get her on TikTok, eventually.” She then added: “I doubt it.”