Match of the day:  Iga Swiatek (POL) vs.  Jelena Ostapenko (LAT)
The rematch is finally here.
Back in February 2021, Jelena Ostapenko was the last player to defeat Iga Swiatek before the Pole embarked on a historic 37-match winning streak and ascended to World No.1, a position she has held ever since. That 4-6, 6-1, 7-6(4) victory in the second round of Dubai, a title Ostapenko went on to win, gave the Latvian a 3-0 head-to-head record against Swiatek. Ostapenko remains the only player who has faced Swiatek multiple times at tour level and never lost to her. They have not played since.
It's been anticipated on a number of occasions. The following week, the pair were one match away from meeting in the Doha final, only for Ostapenko to fall to Anett Kontaveit in her semifinal. Across the rest of 2022, they were projected to face each other in the Miami quarterfinals, Roland Garros and US Open fourth rounds, and Cincinnati third round. Ostapenko lost prematurely each time.
In 2023, it's been the other way round. They were one match from playing in the Australian Open quarterfinals and Rome semifinals, but this time it was Swiatek who didn't come through, losing to Elena Rybakina both times. They could have also met in the Miami fourth round; Ostapenko made her allotted slot, but Swiatek withdrew from the tournament due to a rib injury.
After all those near misses, it's finally time for this intriguing rivalry between two Roland Garros champions to restart. Can Ostapenko truly be labelled Swiatek's nemesis? How transformational has Swiatek's progress over the last 18 months been? The top seed thinks she's come a long way.
"I learned a lot during these past two years how to play on faster hard courts and how to play against heavy hitters," Swiatek said after a remarkable 49-minute third-round victory over Kaja Juvan. "With Jelena, it's a little bit like one day she can play a perfect match and just put everything in even though she's really risking, and the other day can be different. You never know what to expect. But I kind of accept that all these players, they are going to play the best tennis against me. I felt that couple times already."
That's a dynamic Ostapenko also wants to exploit. She's spoken about feeling more pressure as the higher-ranked player, and consequently has needed three sets to win all three of her matches this week in very on-brand rollercoaster scorelines. By contrast, the 26-year-old says she can swing freely as the underdog.
"It's, of course, easier to play when you are not the favorite," Ostapenko said after defeating Bernarda Pera 4-6, 6-3, 6-3. "Especially these three matches that I played, I was the favorite. You have a little bit more extra pressure because you understand that everybody expects you to win. So maybe that's why it was little bit like a rollercoaster. But I think now I can play free because it's great to be in the fourth round. Just enjoy it.
"It's also not easy to be No. 1 because everybody obviously wants to beat you. I probably will take advantage of that."
If Ostapenko succeeds, she'll knock off a significant milestone in her career: quarterfinal-or-better showings at each of the Grand Slams.
Also in action
[WC] Caroline Wozniacki (DEN) vs.  Coco Gauff (USA)
It's fitting that, in the third tournament of her comeback from maternity leave, 33-year-old Wozniacki should face 19-year-old Gauff, the highest-ranked teenager in the world and the form player of the North American hard-court swing.
It's not just the generational intrigue, but the stylistic one. Gauff's base game is comparable to Wozniacki's: centred around astonishing athleticism and footspeed, able to attack with a rock-solid backhand, but exploitable on the forehand side. Gauff's supreme net skills already took the Wozniacki model a step further, and this summer she's worked hard to reinvent her forehand as an aggressive shot.
Wozniacki had notched only one win in two tournaments ahead of the US Open, but a second-round upset of old rival Petra Kvitova has ignited her comeback. The Dane backed it up with a 4-6, 6-3, 6-1 defeat of Jennifer Brady in the third round. Meanwhile, Gauff has needed to come from a set down twice so far, against Laura Siegemund in the first round and Elise Mertens in the third.
 Sorana Cirstea (ROU) vs.  Belinda Bencic (SUI)
American hard courts have become the happiest of hunting grounds for Cirstea this year. The 33-year-old Romanian stunned No.4 seed Elena Rybakina 6-3, 6-7(6), 6-4 in the third round; it was the eighth Top 5 win of her career, four of which have come on U.S. soil in 2023. The result puts Cirstea into the second week of a major for the fifth time, and the first in New York. However, it's now over 15 years since her sole Grand Slam quarterfinal at Roland Garros 2008.
Bencic has also historically thrived in Flushing Meadows. She's in the second week for the fourth time in eight appearances, more than at any other major; previously, she reached the semifinals in 2019 and quarterfinals in 2014 and 2021. Cirstea is an opponent the former World No.4 has struggled with in the past: Bencic lost their first two meetings, and had to come from a set and 5-3 down to notch a first win in the second round of last year's US Open 3-5, 7-5, 6-2.
 Karolina Muchova (CZE) vs. Wang Xinyu (CHN)
Ostapenko isn't the only player with an opportunity to complete the full set of Grand Slam quarterfinals today. That's also on the line for Roland Garros finalist Muchova, who also reached the 2021 Australian Open semifinals and is a two-time Wimbledon quarterfinalist.
The Czech player is yet to drop a set, and faces an opponent making her major second-week debut in No.53-ranked Wang. The 21-year-old Chinese player's form has ticked upwards ever since winning the Roland Garros doubles title alongside Hsieh Su-Wei, with net play an increased feature of her game.
Wang has won 12 of her past 13 matches, including the Landisville ITF W100 title three weeks ago followed by a run to the Cleveland quarterfinals. Meanwhile, Muchova has also won eight of her past nine matches after reaching the Cincinnati final. The pair have not played before.