They are, at first glance, an incongruous doubles team.
Coco Gauff just turned 19 years old and is an amped-up, athletic livewire, whose serves can reach well into the 120s. A decade older, Jessica Pegula is remarkably chill, considering she plays tennis for a living.
And yet, on court together, they mesh perfectly. Gauff says she appreciates Pegula’s calming influence -- and that’s helped this yin-yang partnership thrive. The two Americans recently won the title in Doha, to go with three titles last year, plus a finals appearance at Roland Garros.
The Florida residents are both thinkers, problem-solvers, and (perhaps not coincidentally) happen to be ranked among the Top 10 of Hologic WTA Tour singles players. And, make no mistake, they both want to win this Miami Open -- in what amounts to their backyard.
On Thursday, Day 3, the No.3-seeded Pegula takes on qualifier Katherine Sebov. No.6 Gauff meets Rebecca Marino on a day that features 16 second-round matches from the top half of the draw -- all of them involving seeded players.
Last year, Pegula made it to the semifinals here, overcoming Sloane Stephens, Elena Rybakina and Paula Badosa along the way. And while Pegula fell to World No.1 Iga Swiatek, it was the beginning of a surge that lifted her from outside the Top 20 to the podium of elite players at No.3.
Pegula has been remarkably consistent, reaching the finals at Madrid a year ago, then breaking through with a title in Guadalajara -- both WTA 1000s. She’s advanced to the quarterfinals of five majors in the past three years, including four of the past five.
“It’s so weird to think that I’m three in the world,” Pegula said at Indian Wells. “I don’t even like to say it. It’s awkward. I guess it’s a good thing. Of course, maybe people talk about you more, you become a favorite more. But at the end of the day, I feel like when I’m out there, like that ever doesn’t really enter my mind. What enters my mind is just trying to win the match I’m in.”
Up next is Sebov, a 24-year-old Canadian who came through qualifying. She’s ranked No.172 but is working on an eight-match winning streak (including ITF matches), which includes a three-set upset of Linda Fruhvirtova in the first round. Pegula and Sebov have never played.
While Pegula fell in the Indian Wells fourth round, Gauff got to the quarterfinals, where she lost to eventual finalist Aryna Sabalenka. After the 6-4, 6-0 defeat, Gauff was looking forward to flying back to Florida.
“Definitely helps when you just get bageled, so it’s nice to go home and I guess reset,” Gauff told reporters. “I’m glad that Miami is next and I’m looking forward to that.”
Like Pegula, Gauff is looking to make the next step up in class.
“Right now I feel like I’m playing where my ranking is,” Gauff said, “and I don’t want to stay just inside the Top 10. I want to be No.1. So I think I have to do better when it comes to these types of matchups when I’m playing higher-ranked players or in general even players who are slightly ranked lower than me.”
Gauff holds a 1-0 head-to-head advantage over Marino, going back to last year’s 7-5, 6-0 first-round victory at Roland Garros.
Pegula is 6-3 in three appearances in Miami, while Gauff is 3-3. If the seeds hold, the two Americans would meet in the quarterfinals.
Other notable Thursday matches:
 Elena Rybakina vs. Anna Kalinskaya
Rybakina will attempt to follow up her Indian Wells title with another crown in Miami -- the rare Sunshine Double. Only four women have achieved it -- Stefanie Graf, Kim Clijsters, Victoria Azarenka and Iga Swiatek.
No.64-ranked Kalinskaya is a familiar foe from Rybakina's junior days. Rybakina won their only meeting at that level, on clay in 2014, but Kalinskaya has taken their only pro meeting to date 6-4, 6-4 in the 2019 Playford ITF W25 final. Kalinskaya has a strong history in Miami: two of her nine career Top 30 wins have come at this tournament, including a second-round upset of Karolina Pliskova last year.
Camila Giorgi vs.  Victoria Azarenka
Azarenka is a three-time Miami Open winner, going back to her first title -- as a 19-year-old in 2009, when she stunned World No.1 and defending champion Serena Williams 6-3, 6-1. Williams accumulated the most match-wins in Miami of any player at 76, and Azarenka (38) is the only active player on the Top 10 list.
Giorgi is a tenacious opponent. She’s coming off a three-tiebreak victory against Kaia Kanepi, a match that ran 3 hours, 32 minutes -- equaling the longest women’s match of the year. She holds a 2-1 head-to-head advantage in this 30-something matchup, but the two haven’t played since 2019.
Elise Mertens vs.  Daria Kasatkina
Kasatkina lost her second match in Indian Wells to qualifier Varvara Gracheva, while Mertens fell in the first round to Wang Xinyu.
Although she’s only 5-7 for the year, Kasatkina holds a formidable 4-1 head-to-head edge against Mertens, the most recent match a straight-sets win in last year’s Sydney Round of 16.