Ija Swatik, the top seed at the US Open, loses in the fourth round

When world No. 1 Ija Swiatek won the first set against Jelena Ostapenko on Sunday night, it was business as usual.

Vswiatek, a four-time Grand Slam champion at the age of 22, was the reigning US Open champion and, prior to her match against Ostapenko, had not dropped a set in this tournament.

But while Swiatek is often able to get around matches, Ostapenko has been a thorn in her side. Ostapenko was undefeated against Swatik, and extended that to four wins with a victory Sunday night 3-6, 6-3, 6-1.

In the second set, the game changed. Ostapenko began to take control. And when Ostapenko leveled things off with one set, Swiatek seemed to be out of her comfort zone.

As she struggled, Swiatek looked at her chest, seemingly asking for some kind of advice for dealing with Ostapenko’s augmentation. Her coach, Tomasz Viktorowski, seemed to have no answer for her, and Swiatek sarcastically clapped her chest, as if to thank you for nothing.

Throughout the third set, Ostapenko was relentless. “I had to be aggressive because that’s what she really doesn’t like,” Ostapenko said in an on-court interview after the match. “I’ve been fighting to the last point.”

Ostapenko will now face American No. 6 Koko Gauff in the quarterfinals on Tuesday. Gauff also recently found out how to beat Swiatek after beating her in the semifinals of the Western & Southern Open in Ohio last month.

Ostapenko and Gauff have faced each other twice, most recently at the Australian Open, where Ostapenko defeated Gauff in straight sets in the round of 16. Gauff won their previous match in 2019.

“It was a tough match,” Ostapenko said of her Australian Open match against Gauff earlier this year. “Of course, it will be another tough match. I don’t expect any easy matches here in a Grand Slam, so I’m ready for another battle.

But now, without Swiatek in the way, the US Open women’s singles draw is open on a much larger scale. Suddenly, the road to the final became easier for Ostapenko, Gauff, Jessica Pegula, Onnes Jabeur and Aryna Sabalenka.

Gauff is ready to take on Ostapenko, who she described on Sunday as a strong player ahead of Ostapenko’s win.

“With Jelena, she’s attacking and attacking with the ball. I lost to her at the Australian Open this year. She’s either hot or cold to be honest,” said Gauff.

The winner of Ostapenko and Goff will face the winner of the quarter-final match between Sorana Cirstea and Karolina Muchova in the semi-finals. Romanian Cirstea advanced to the quarter-finals after defeating 15th seed Belinda Bencic on Sunday. Muchova, who reached the French Open final this year, advanced to the quarter-finals after dropping just one set in four matches.

For now, Ostapenko is focusing on Goff, who she expects will pose a tough challenge.

“I’ll try to focus on myself and have fun,” Ostapenko said. “It’s great to be in the quarter-finals, especially here in New York.”