How six of tennis’ early-season surprises might fare the rest of 2017

“Who are you?” is the question of the moment in tennis.

This weekend, Elina Svitolina beat world No. 1 Angelique Kerber on her way to winning the biggest title of her career, in Dubai; in the process, she ran her 2017 record to 17-2. Jo-Wilfried Tsonga, who hadn’t won a title since 2015, won his second straight, in Marseille. And Jack Sock, the new American No. 1, won his second event of 2017, in Delray Beach.

Those aren’t the only players suddenly surging. So far this year we’ve seen Grigor Dimitrov win two events and reach the semifinals at the Australian Open; Karolina Pliskova win two of her own and rise to No. 3 in the world; and Caroline Wozniacki, who, like Tsonga, seemed to be on a slow but irreversible career slide, reach the finals in Doha and Dubai.

Most of these surprises have been pleasant ones. The players involved are either crowd favorites or young talents who have yet to fulfill their considerable potential. It’s been a thrill to see Dimitrov, at 25, remind us why he’s such an exciting player to watch, and to see Pliskova, at 24, begin to take herself seriously as a major-title contender. And tennis is always better when Jo is jumping for joy.

Now that February is about to turn to March, the next question needs to be asked: How much will any of this matter when we get to the business end of the season this spring? In 2016, the title-winning players in February were Roberto Bautista Agut, Roberta Vinci, Nick Kyrgios, Venus Williams, Dominic Thiem, Sara Errani, Kei Nishikori, Carla Suarez Navarro, Martin Klizan, Sloane Stephens, Sam Querrey, Heather Watson, Stan Wawrinka, Pablo Cuevas and Svitolina. Of those, only Wawrinka went on to reach a Slam final. For the most part, February’s heroes peaked early.

Are 2017‘s fast starters destined to slow down, too? Here’s my assessment of the long-term viability of the year’s early winners, in ascending order of promise.

Jo has won back-to-back titles, and just as impressive is the list of players he beat to win them: Marin Cilic, Tomas Berdych, David Goffin, Kyrgios and Lucas Pouille. In the final against Pouille in Marseille, Tsonga didn’t face a break point and served out the last game at love. There’s nothing I’d like to see more than for the personable and athletic Frenchman to keep it up. But at 31, and with the U.S. hard-court swing coming up, it seems unlikely. Jo has never done his best work in Indian Wells or Miami; in nine seasons, he has yet to get past the quarterfinals at either event. But if these two wins give him a little more confidence that he can still compete for the Roland Garros title in June—and they might—they won’t have gone for nought.

Svitolina is 17-2 this year, has won two titles and has debuted in the Top 10. It all seems right on time; the Ukrainian, who upset Serena Williams at the Rio Olympics last summer, is entering what should be her prime at 22. In Dubai, she beat Kerber for the third straight time and ran away from Wozniacki in the second set. Svitolina isn’t towering, and she’s not a ball basher, but in those two matches she showed that she can take over the points against even the WTA’s most dogged defenders. Still, the fact that Svitolina isn’t a towering ball basher will force her to work harder, and be more consistent, for longer. I could see her making a Slam semi, and also coming back down to earth elsewhere.

By last summer, Wozniacki’s ranking was down to No. 58, and there were rumors that her retirement was imminent. What a difference a U.S. Open can make. Since reaching the semifinals at Flushing Meadows, Wozniacki has won titles in Tokyo and Hong Kong, reached the finals in Doha and Dubai back to back, and rejoined the Top 15. At 26, she seems to have a second career ahead of her, if she wants it. Maybe Serena’s old hitting partner, Sascha Bajin, who Wozniacki has been working with, can bring something new to her tried-and-true baseline game. Still, judging from her final-round losses to Pliskova and Svitolina, each of whom had their way with the rallies, Wozniacki’s ceiling is no higher than it ever has been.

“Ambling into History” is the title of a George W. Bush biography, and that’s what Sock seems to be doing at 24. The Kansas native cruises around the court with his hat perched high and backwards—and slightly out of place on his head—yet he keeps cruising forward in the rankings. In 2017, he has won titles in Auckland and Delray Beach and cracked the Top 20, and he looks like he’s going to be the No. 1 U.S. male player for the foreseeable future. It’s almost as if Sock, who can take the long road to victory, keeps surprising himself with what he can accomplish. With his serve, forehand and speed, the sky—or at least the Top 10—would seem to be the limit. The next step is to reach the quarterfinals at a major; he hasn’t been there yet, but if he can snag a Top 16 seeding, the French Open would seem to be the time and the place to make it happen.

Dimitrov is 16-2 with two titles and a Slam semi, and he looks poised to break back into the Top 10 for the first time in three years. That’s how it should be for a player with his gifts and skills. As far as how Dimitrov does the rest of the season, we should start by defining what would qualify as success for him. Is it to win his first Masters title? Reach another Slam semi? Stay in the Top 10? Keep his level high from week to week? Beat the guys in the Top 5? Win a major? There are those who, watching his game and remembering the attention he has generated over the years, would say that anything short of a Slam win is a failure from him. And if Dimitrov ends his career Slam-less, it will be a disappointment. For this season, though, I want to see him be part of the mix of contenders in the same way that the players in the Top 5, 6 or 7 are—consistently. Deep runs at the majors and a Masters title would be satisfactory for the moment. He has come too far, and is playing too well, to do anything less.

Pliskova is 15-2 in 2017, and has established herself at No. 3 in the world. Of all the players here, the 2016 U.S. Open runner-up would seem to be the most likely Slam winner in the immediate future. She has a game that can blow virtually anyone off the court on the right day, and, even more so than Sock, the 24-year-old has begun to realize it. With her own expectations on the rise, Pliskova is in roughly the same place that Garbiñe Muguruza was at the start of 2016. As we know now, things worked out well for the Spaniard at the French Open, but not so well anywhere else. There will be peaks and valleys for Pliskova as well; like Muguruza, she plays with dangerously little margin for error. Over the last six months, though, Pliskova has taken that U.S. Open finalist trophy and run with it. How far she runs over the next month, on slower U.S. hard courts, will be one of the storylines of the spring.