Iga Swiatek's US Open title defense and stay at No. 1 end with a loss to Jelena Ostapenko

WATCH: Jelena Ostapenko Hooks Up Fan With Ticket After DM Request, Then Dethrones Iga Swiatek | US Open

NEW YORK (AP) — Iga Swiatek arrived at the U.S. Open as its reigning champion, as the winner at three of the past six Grand Slam tournaments and as the owner of the No. 1 ranking for nearly one and a half years.

None of that mattered on Sunday night against Jelena Ostapenko, whose powerful style disrupts Swiatek's rhythm — and beats her every time.

Swiatek's title defense at Flushing Meadows ended in the fourth round with a 3-6, 6-3, 6-1 loss to 2017 French Open champion Ostapenko in the fourth round at Arthur Ashe Stadium. The result also means Swiatek's stay at atop the WTA will end next week, when current No. 2 Aryna Sabalenka will rise to the top spot for the first time.

"There are some sad emotions" about falling from No. 1, Swiatek acknowledged, while also saying of her reign atop women's tennis: "It was pretty exhausting."

Not long after being assured of losing her grip on that perch, the 22-year-old from Poland already was thinking ahead to returning there.

"For sure when I'm going to be, next time, in the same situation, I'm going to do some stuff differently," Swiatek said, "because it was a little bit stressful, and it shouldn't be."

She also sounded mystified about what happened out there Sunday.

"I'm just surprised that my level changed so drastically, because usually when I play bad, I play bad at the beginning, then I kind of catch up or just problem solve. This time it was totally the opposite," Swiatek said. "I don't really know what happened with my game. I felt no control suddenly."

The 20th-seeded Ostapenko, a 26-year-old from Latvia, offered a theory.

"The main thing is that she doesn't really like to play against big hitters. ... She likes to have some time," said Ostapenko, who accumulated 31 winners to 18 for Swiatek. "When I play fast, aggressive and powerful, she's a little bit in trouble."

Ostapenko also finished with just 20 unforced errors—quite an improvement from the 80 she had in her second-round victory last week.

When a reporter mentioned Sunday's total, Ostapenko smiled and said, "Not bad."

In truth, this was not necessarily a huge surprise, based on their previous matchups: Ostapenko improved to 4-0 against Swiatek over their careers. No other player owns four victories against the woman who has led the WTA rankings since April 2022.

After getting off to a terrific start to the second set, which she led 4-1, Ostapenko wavered for a bit. That allowed Swiatek to get a break back and pull to 4-3.

But that was only a blip.

With Swiatek having trouble serving—perhaps owing to all of the squeaking Ostapenko's shoes did as she moved around during the ball toss while waiting to return—the contest quickly tilted in one direction. Ostapenko reeled off seven consecutive games to go up 5-0 in the third set.

Ostapenko broke one last time to end it, meaning she won seven of Swiatek's 13 service games in the match.

And Swiatek could not explain why she did not have that same amount of mistakes against Ostapenko's serve.

"My mistakes were so huge, and I had no idea why suddenly I couldn't return," Swiatek said. "I'm a good returner."

Ostapenko's first quarterfinal at Flushing Meadows will come against Coco Gauff, the 19-year-old American who eliminated Caroline Wozniacki 6-3, 3-6, 6-1 earlier Sunday.

Ostapenko and Gauff have split two previous meetings. The most recent came in the fourth round of the Australian Open in January, and Ostapenko won that one.

"She's a great young player," Ostapenko said about Gauff. "Of course it's going to be another tough match. I don't expect any easy matches at a Grand Slam."