Match of the day:  Iga Swiatek (POL) vs. [Q] Kaja Juvan (SLO)
Iga Swiatek and Kaja Juvan go back a long way.
They met nearly a decade ago as 13-year-olds just starting their journeys in the sport at Tennis Europe's Summer Cups in 2014. They won the doubles gold medal together at the 2018 Rio de Janeiro Youth Olympic Games. And now, they'll play off for a place in the second week of the US Open.
"She's my best friend on tour," said defending champion Swiatek after defeating Daria Saville in the second round. "She's one of the most honest and I think smart people on tour."
As juniors, Swiatek and Juvan bonded over their love of reading -- Swiatek preferred history, Juvan was into philosophy -- and now, Swiatek says, they share "everything" with each other. They've already gone out for dinner together in New York, despite knowing they were in each other's section of the draw.
"We know how to keep it cool," said Swiatek. "We already played couple of times against each other. I think we both can kind of cut off the off-court friendship and just play our game, and then we are friends back.
"I think we both know how to be professional and just play the match and that's all."
Juvan's journey to the third round has been a testament to the Slovenian's resilience. She was ranked at a career-high of No.58 just over a year ago, but her tennis took a back seat after her father, Robert, died of stomach cancer in December. After initially attempting to keep playing this year, Juvan announced an indefinite break from the tour in April.
Weeks later, she returned with a ranking of No.244 -- but also a fresh perspective, and rejuvenated results. Juvan qualified and made the second round of Wimbledon, reached the Budapest quarterfinals, and is now in the third round of a major for the fourth time after surviving five match points in her final qualifying round against Himeno Sakatsume.
Swiatek has won both of their tour meetings to date, both in 2021, though neither were wholly straightforward: 2-6, 6-2, 6-1 in the second round of the Gippsland Trophy and 6-0, 7-5 in the first round of Roland Garros. Juvan's quest for a maiden Grand Slam second week may have to wait. But the pair's enduring friendship will ultimately be what matters.
Three more to watch
 Karolina Muchova (CZE) vs. Taylor Townsend (USA)
As a pure tennis show, few matchups promise more than this one, which pits Roland Garros and Cincinnati finalist Muchova against Cincinnati doubles champion Townsend. The pair are two of the most gifted, creative shotmakers on tour, and particularly effective in the forecourt. In two matches so far this week, Muchova has won 23 out of 33 net points, while Townsend has been successful on 46 out of 57 ventures forward.
The pair have never played before, which makes it even more of a must-watch prospect.
More from the US Open:
- Oops! Coco Gauff forgets the score in opening doubles win
- Taylor Townsend is ready for her close-up
- US Open fashion: Inside the trendsetting pieces in New York
- WTA and Morgan Stanley host kids clinics in Harlem
[WC] Caroline Wozniacki (DEN) vs. Jennifer Brady (USA)
A battle of the comebacks: the US Open is former World No.1 Wozniacki's third tournament of her return from maternity leave after an absence of three-and-a-half years, and former Australian Open finalist Brady's fifth tournament after being sidelined for one-and-a-half years due to plantar fasciitis.
Brady, now ranked No.433 and entered on a protected ranking, has already notched three wins over Top 30 players since coming back, including a 6-1, 2-6, 6-2 upset of No.24 seed Magda Linette in the second round. Meanwhile, No.623-ranked Wozniacki edged No.11 seed and old rival Petra Kvitova 7-5, 7-6(5) for her third victory of the month, and first over Top 100 opposition. This will be their first meeting.
 Elise Mertens (BEL) vs.  Coco Gauff (USA)
Cincinnati champion Gauff is on a seven-match winning streak, the third-longest of her career so far, after a pair of quality wins over Laura Siegemund and Mirra Andreeva. She's won both of her previous meetings against Mertens, but will still have to be sharp against the gritty Belgian. Two-time quarterfinalist Mertens is playing with house money twice over after saving three match points in her first round against Mirjam Bjorklund, then two match points in her second round against Danielle Collins.
Also in action
Former Wimbledon champion Elena Rybakina, who received a walkover from Ajla Tomljanovic in the second round, bids to improve a perfect 2-0 record against No.30 seed Sorana Cirstea.
No.15 seed and 2019 semifinalist Belinda Bencic takes on the much-improved Zhu Lin, who knocked out three-time finalist Victoria Azarenka in the second round 6-3, 6-3. Zhu will be aiming to reach the second week of a major for the second time this year, following the Australian Open.
No.20 seed Jelena Ostapenko struggled to put away Elina Avanesyan's defense in the second round, letting leads of 5-2 in the second set and 5-3 in the third slip before coming through 6-3, 5-7, 7-5. The Latvian faces a very different stylistic challenge against big-hitting Bernarda Pera, who won their only previous meeting on Ostapenko's home soil at Jurmala 2019.
A debut in the US Open second week is at stake as No.53-ranked Wang Xinyu takes on No.64-ranked Anna Karolina Schmiedlova for the first time. Wang is aiming to make the fourth round of any major for the first time, having reached the third round for the first time at Roland Garros this year. Meanwhile, Schmiedlova has her sights set on a fourth-round place for the second time in the last three Slams after hitting that milestone for the first time at Roland Garros.