NEW YORK -- At the US Open on Saturday, Caroline Wozniacki stepped up to the baseline for her opening service game. Then she did what she almost always does.
On the first point of her match with Jessika Ponchet, Wozniacki served out "wide" to her opponent's forehand. On the next two points, she aimed serves down the center line, or the "T." On the fourth point, she went wide on the ad court. Wide, T, T, wide.
It's a pattern that Wozniacki, remarkably, has been repeating with very little deviation for several years. When her first serve misses its intended mark, it's less rigid -- she might change the service direction then -- but on first serve, for the first four points of each game, the pattern is often the same.
If a game goes beyond four points, Wozniacki changes to something seemingly more random. According to analysis from TennisAbstract.com in 2019, she stays true to her plans around 80% of the time.
Against Nao Hibino in Round 1 in New York on Tuesday, Wozniacki made just one change from her routine in the first set, aiming into the body on the second point at 4-0. In the second set, she made only two clear switch-ups. Hibino, who had never played Wozniacki before, was crushed 6-0, 6-1.
In the second round, against Renata Zarazua, she made just two clear changes in the first set. Against Ponchet in Round 3, she made only four deviations in the first set. In the opening game of the second, she changed her pattern completely, to T-wide-wide-T, but she soon returned to the plan, with just one exception.
At Wimbledon this year, it was much the same story. In her first-round win over Alycia Parks, Wozniacki went wide-T-T-wide on the first four points every time in the first set. Against Leylah Fernandez in the second round, she changed only once in the first set. There were more changes in the second and third sets, but even then, she stuck to the blueprint on the first four points 28 times out of 40. In her 15 service games, her first serve was aimed wide 14 times.
Maybe Elena Rybakina got the message in Round 3, when she beat Wozniacki 6-0, 6-1. Outplayed in the first set when she deviated four times, the former world No. 1 changed things up a lot more in the second, but it didn't help.
In an era when comprehensive data is readily available, Wozniacki's patterns are easily discoverable by her opponents and especially by their coaches. The 34-year-old turned down requests from ESPN to discuss her thinking, but she doesn't seem to be worried that players might know where she's going to serve. In three matches so far here this year, she has dropped just 12 games.
Through to the fourth round for the second year in a row, Wozniacki plays either Anna Kalinskaya, the No. 15 seed, or the No. 22, Beatriz Haddad Maia, and seems to be saving her best form for the Grand Slams.
Many of those who have coached against Wozniacki know the pattern or at least part of it. Mike James, a renowned data analyst on the tour, said he thinks most leading coaches on the WTA Tour must know by now.
"Nowadays you have so many different ways to find the serve patterns," he said. "There are many private companies that are delivering analytics, plus analysts that are using the WTA/ATP Grand Slam data. Anybody nowadays should be doing their homework around serve patterns."
It is to Wozniacki's credit, then, that she has been so successful, even when her intentions are so clear. James, who previously worked with Iga Swiatek and who has been helping Coco Gauff and Victoria Azarenka at the US Open, says that's partly because direction is not the only thing a returner needs to focus on.
"Often players are going to what is comfortable when they're uncomfortable, so I can understand [why Wozniacki does what she does]," he said. "If it's comfortable enough, where they're winning enough, then why change it? It comes down to ball quality. If the ball quality and accuracy is there, then keep doing it."
Wozniacki returned to the sport in 2023 after three years out, during which she had two children. She was world No. 1 in the year-end rankings for two straight years, in 2010 and 2011, and has won 30 titles in all, including the Australian Open in 2018. Even then, in an epic three-set final with Simona Halep, she largely followed the pattern.
On the face of it, knowing where an opponent is likely to serve should be a huge advantage to the receiver. But perhaps it's just pragmatism on the part of Wozniacki. The serve has never been the strongest part of her game, so if adhering to a pattern is what makes her comfortable, then fair enough. With her outstanding movement and brilliant backhand, she backs herself to win the point anyway.
Why would a player not change an obvious pattern? "[Because] they're really good at it, and they trust it," said Craig O'Shannessy, a strategy coach and analyst for ATPTour.com. "When things get tight and nervous, they know they can make that serve."
O'Shannessy uses eight filters to detail what players do when they step up to serve, including what the opponent thinks they're going to do, where the server wants the ball to come back, what the score is and what conditions the match is being played in.
"Sometimes you could even tell the opponent, I'm serving wide, because it's my highest-percentage pattern or favorite pattern," he said. "If you get enough of those filters leaning your way, it helps you and it doesn't matter what they know."
And even when a player does know where the ball is likely to go, that's no guarantee of success. "The last thing you want is a player to turn around and say, hey, you told me he was going to serve there," he added.
"The way I would present it is to say, 'This is where he wants to go.' I coached one player here on Ashe against Roger Federer. I told him, 'He likes to go wide, look for it wide.' First point of the match, Fed goes right down the center and the guy looks at me and stands there [with his arms wide open] for about five seconds. The match was over in his head right there."