MASON, Ohio — Before this summer, Kiki Bertens was perhaps the closest thing modern women’s tennis had to a clay-court specialist.
She had won five WTA titles, all on clay, the most recent this April in Charleston, S.C. The biggest final of her career was on the clay of Madrid. Her best Grand Slam result was a run to the semifinals of the 2016 French Open, where she lost a close two-set battle to Serena Williams.
Away from her preferred dirt, Bertens had an 0-11 record against top-10 players and had not reached the final of any grass or hardcourt tournament.
But after strong results at Wimbledon and on North American hard courts, Bertens, 26, heads to New York as a contender for the United States Open title.
Ranked 17th, Bertens has reeled off an 8-0 record against top-10 players on grass and hard courts this summer. She beat Venus Williams and Karolina Pliskova at Wimbledon, then beat Pliskova and Petra Kvitova in Montreal two weeks ago.
Last week in Cincinnati, Bertens marched to the biggest title of her career by ousting four top-10 players: No. 2 Caroline Wozniacki, No. 7 Elina Svitolina, No. 6 Kvitova and No. 1 Simona Halep.
In Sunday’s final, Halep, who has tightened her grip on the top spot in the rankings with strong play this summer, looked on track for a straight-sets win. But Bertens saved a championship point in the second-set tiebreaker to force a third set. When Bertens took an early lead in the third set, Halep, who was playing her 10th match in 12 days after winning the title in Montreal the week before, faded quickly.
Bertens closed the win by hammering an ace down the middle of the court, screaming in delight, her knees sinking onto the hard surface that had once tormented her.
“Normally I’m really looking forward to the clay court season,” Bertens said. “So, O.K., I’m looking forward to that again next year, but it’s such a great feeling that you can play on other surfaces really well, as well, and that you can win tournaments like this, also.”
Bertens, who is from the Netherlands, came close to not playing any tournaments this year. She seriously considered retiring from the sport after a miserable finish to last season.
“I was really not happy with the way I felt,” she said. “I was like, O.K., I don’t want to continue like this. So if I have to feel like this all the time on the court, it’s better to stop.”
Her coach, the former Dutch player Raemon Sluiter, even encouraged her to stop if she was not enjoying her tennis, which she clearly was not.
“It’s a terrible word that all the coaches use, but I like to watch the process, and not necessarily the results,” Sluiter said. “In the end, it’s about results, but I trust in the process — and the process was shocking. She couldn’t find the energy to work. If she had a few victories, even on clay, it was just relief instead of excitement when she did something.”
Bertens played on in order to qualify for the year-end championships in doubles with Johanna Larsson, but Sluiter grew frustrated with her attitude.
“I said, well, I’m not going to continue like this, and I strongly advise you that with the way you feel, you also quit,” he said. “She was No. 32 in the world, but if it doesn’t make you happy, it’s not worth it.”
Sluiter and Bertens took vacations, separately, on opposite sides of Bali. When they got back in touch, Bertens presented a list of things she wanted to change. Sluiter, who normally had to take the initiative in their coaching relationship, was impressed.
“That was for me the point where she was taking things more in her own hands,” he said. “I’m on board again. From that point on, when we started practicing in the off-season last year, beginning of December, I think there hasn’t been one bad day. That’s the biggest thing.”
Sluiter said in the past after a tough loss Bertens would start stress eating and not wanting to practice.
“She would lose a week by doing the wrong things,” he said. “And then to recover from those wrong things, she would need three more weeks, so it was very up-and-down.”
At the Miami Open in March, she lost a close three-set match to Venus Williams in the round of 32. “The next day she’s on the treadmill,” Sluiter said, “and the day after she’s practicing on clay for Charleston. That has been the most important thing from this year.”
Turning her Cincinnati success into U.S. Open success will not come easily. Finding New York draining, Bertens will stay away from the city as long as she can before the tournament. She will try to take walks in Central Park, and find quiet coffee shops when possible, to avoid the cacophony of the city.
Though she performed well in Cincinnati’s biggest court, Sluiter acknowledged that playing under a magnifying glass as the champion of one of the biggest U.S. Open lead-in tournaments may be unpleasant for Bertens, a shy player who prefers shunning the spotlight.
“If she can choose if she plays on Center or Court 19, it’s going to be Court 19,” he said.
“But if she takes it as it comes, it’s fine. Of course people are going to look a little bit more at what she’s going to do, but if you’re good enough, you’re good enough. And if you’re not, you’re not.”