Match of the day:  Elina Svitolina (UKR) vs.  Jessica Pegula (USA)
Over the past few years, Jessica Pegula has entrenched herself in the Top 5 by developing a near-unmatched reputation for consistency.
Since the resumption of the tour following 2020's Covid shutdown, Pegula has competed in 35 WTA 1000 and Grand Slam tournaments, and reached at least the quarterfinals in 20 of them. Regardless of the surface, the continent, the balls, the weather conditions, the American is always there, working her way through draws with relentless professionalism.
In a sense, she's a successor to Elina Svitolina. Between 2014 and 2021, the Ukrainian racked up 30 quarterfinal-or-better finishes at WTA 1000, Olympic and Grand Slam level (plus a WTA Finals title in 2018 and runner-up place in 2019). Like Pegula, she dealt in unflappable baseline consistency and capable but unflashy all-court skills.
Like Pegula, Svitolina also faced questions over her ceiling in the game. Pegula has won two WTA 1000 titles, including Montreal three weeks ago, but lost all six of her Grand Slam quarterfinals to date. Svitolina also lost her first four major quarterfinals, and had been a Top 10 player for over two years -- and a WTA Finals and four-time WTA 1000 champion -- before breaking through to a Grand Slam semifinal at Wimbledon 2019.
It was somewhat fitting that when the pair met four weeks ago in the Washington quarterfinals that the match turned out to be a thriller. The queens of consistency showed off their full repertoires -- both attacking and defending, excelling at the baseline and at net -- before Pegula edged it 4-6, 6-3, 6-4.
The quality of that match was a testament to how successful both have been at reinventing themselves of late. Pegula's Montreal title run featured a semifinal win over Iga Swiatek that could prove a significant turning point in her career. Meanwhile, Svitolina has returned from maternity leave this year with a newly aggressive mindset and determination to stay on the front foot.
"I always was looking to improve my serve, to improve the power on my shots, to strike the ball more cleaner, some technical things on my forehand," she said after defeating Anastasia Pavlyuchenkova 5-7, 6-4, 6-4 in the second round. "Now I had time. I had three months starting from January until my first match where we were just working on my game."
Svitolina has been involved in some of the most riveting Grand Slam contests of 2023, and one of their characteristics is the tension as the 29-year-old sways between her old habits and her new approach. Against Pavlyuchenkova here, and against Swiatek and Victoria Azarenka at Wimbledon, there were moments late in the contests where Svitolina forced herself to hit harder, move forwards, take the ball earlier -- and they paid off with victory each time.
But against Pegula, an opponent who's now beaten her three straight times, Svitolina won't be able to afford any moments where she takes her foot off the pedal.
Three more to watch
 Ekaterina Alexandrova vs.  Marketa Vondrousova (CZE)
Despite being the newly crowned Wimbledon champion, Vondrousova is making her way as unobtrusively through the draw this week as she did in SW19. The Czech has dropped just seven games in two rounds, has now won nine straight Grand Slam matches and takes a 3-1 head-to-head advantage into her next contest against Alexandrova. That includes a high-quality 4-6, 6-3, 6-2 win in the first round of Adelaide 1 in January, their only previous meeting on outdoor hard courts.
The big-hitting Alexandrova is a threat, though. She's coming off a run to the Cleveland final last week, and two quality wins here over Leylah Fernandez and Lesia Tsurenko (against whom she overcame a 0-4 record to beat for the first time). Alexandrova also broke through a significant milestone at Wimbledon, making her Grand Slam fourth-round debut on her 26th attempt -- something that could boost her confidence at a stage that had hitherto been tricky for her.
 Ons Jabeur (TUN) vs.  Marie Bouzkova (CZE)
"I think I'm going to use 'warrior' as a symbol for this tournament to continue to the end," said Jabeur after defeating 18-year-old Linda Noskova 7-6(7), 4-6, 6-3. It was a second straight hard-fought win over a dangerous opponent for the Tunisian, who has been battling sickness this week in New York.
Jabeur's draw hasn't let up, though. Bouzkova is one of the most indefatigable defenders on tour, stretched Jabeur to three sets in their only previous meeting (in the 2022 Wimbledon quarterfinals), and is a litmus test for any opponent's fitness.
 Daria Kasatkina vs. [Q] Greet Minnen (BEL)
Fittingly, Pride Day at the US Open saw two of the leading LGBTQ+ representatives on the Hologic WTA Tour set up a third-round meeting. Kasatkina came from a set and a break down to defeat Sofia Kenin 2-6, 6-4, 6-4, while qualifier Minnen backed up her opening win over Venus Williams by beating Sachia Vickery 6-3, 4-6, 6-4.
The pair have played once before, a hard-fought 6-7(4), 6-4, 6-2 win for Kasatkina in the first round of Granby 2022 en route to her sixth and most recent title. Kasatkina is bidding to reach the fourth round of the US Open for just the second time in her career following her 2017 run; Minnen, in the third round of a major for the second time following the 2021 US Open, is aiming for a second-week debut.
Also in action
No.14 seed and Montreal runner-up Liudmila Samsonova faces No.17 seed and 2017 US Open finalist Madison Keys in a clash of two of the tour's biggest hitters. They've split two previous meetings, both of which went to three sets; Keys took their only hard-court encounter 6-3, 3-6, 6-3 in the 2022 Adelaide quarterfinals.
No.2 seed Aryna Sabalenka continues her quest for the World No.1 ranking against Lausanne finalist Clara Burel. There's a sense of déjà vu about Burel's tournament: for the second year in a row, she has knocked out the No.25 seed (last year Elena Rybakina, this year Karolina Pliskova) en route to facing Sabalenka in the third round. But the Frenchwoman will be hoping that doesn't extend to the scoreline, an emphatic 6-0, 6-2 win for Sabalenka last year.
Highlights: Stearns d. Boulter, 2023 Austin R1
Back in February, Peyton Stearns earned her first WTA main-draw win in memorable fashion, battling past Katie Boulter 7-6(5), 6-7(2), 7-6(5) in 3 hours and 22 minutes in the first round of Austin. Since then, Stearns has made her first WTA final in Bogota, Boulter has won her first WTA title in Nottingham and the pair will play again for a maiden Grand Slam fourth-round spot.
No.23 seed Zheng Qinwen will bid to reach the fourth round of a major for the second time against Lucia Bronzetti, who is making her third-round debut. Zheng won their only previous meeting 6-2, 6-3 in the first round of Monterrey 2022.