Five of the world's Top 10 hit the courts for the second round of the US Open on Thursday.
World No.1 Iga Swiatek cruised past 2017 champion Sloane Stephens on Arthur Ashe Stadium. Here is how the rest of the Top 10 did on Day 4:
Petra Martic def.  Paula Badosa 6-7(5), 6-1, 6-2
Croatia's Martic knows what it takes to rack up victories at Grand Slam events. The former Top 15 player has reached the Round of 16 or better at each of the four Grand Slam tournaments; nine times in total including fourth-round runs at the US Open in 2019 and 2020.
However, Martic was only 1-12 against Top 5 players on hard court entering her second-round clash with World No.4 Badosa. Once Badosa eked out the hour-long first set, improving to a splendid 13-2 in tiebreaks this season, Martic was close to another exit against Top 5 opposition on this surface.
Martic, though, rebounded with aplomb to sweep through the last two sets and earn the fourth Top 5 win of her career overall after 2 hours and 5 minutes of play. The 31-year-old was overwhelming down the stretch, totaling 20 winners to just nine unforced errors spanning the second and third sets.
Martic will face another marquee name in the third round: No.26 seed Victoria Azarenka, who beat Marta Kostyuk 6-2, 6-3. Former World No.1 Azarenka, the US Open runner-up in 2012 and 2013, won her only prior meeting with Martic, which was ten years ago on the indoor hard courts of Linz.
 Jessica Pegula def. Aliaksandra Sasnovich 6-4, 6-4
Sasnovich came into the year's last major in good form, having reached the Cleveland final last week. She moved up to World No.32 in Monday's rankings, slightly too late to claim a seeding spot in New York. She is only two spots behind her career-high ranking of No.30.
However, American No.1 Pegula, a quarterfinalist at this year's Australian Open and Roland Garros, was able to bring Sasnovich back down to earth in 1 hour and 19 minutes on Louis Armstrong Stadium on Thursday.
"I'm glad I got through my first two matches doing what I needed to do and playing smart," Pegula said afterward. "It's only going to get tougher from here, so I'm just happy with each match and hoping the next match kind of goes the same way. Try not to get too ahead of myself."
World No.8 Pegula had six aces and converted five of her 10 break points to reach the US Open third round for the third straight year. A love break for 5-4 in the second set proved decisive for the American, and Pegula finished the match by sweeping 12 of the last 13 points.
Pegula, who is seeking her first trip to the US Open Round of 16, will next face qualifier Yuan Yue of China, who bested Irina-Camelia Begu 6-3, 7-6(6).
 Garbiñe Muguruza def. [Q] Linda Fruhvirtova 6-0, 6-4
Muguruza continues to show signs of life at the only major event where she has yet to reach the final, notching a 1-hour and 9-minute win over 17-year-old qualifier Fruhvirtova, who was making her Grand Slam main-draw debut this week.
Muguruza is still only 11-10 at the US Open, and she is just 11-14 in the 2022 season. But after two straight-sets wins over two of the rising teenagers on tour this week, the former World No.1 has some momentum behind her.
The Spaniard was unbothered in the opening set, where Fruhvirtova hit zero winners and won only five points in total. The Czech teen rebounded to take a 4-1 lead in the second set, but Muguruza's experience served her well as she claimed the next five games to triumph.
"I started playing very well, very concentrated, and very composed," Muguruza said. "Obviously in the second set I think she elevated her game, start to hit good groundstrokes and got me a little bit out of place. Luckily I stayed strong there at the end of the second set and managed to close it."
Muguruza will meet her fellow two-time Grand Slam champion Petra Kvitova in a blockbuster third-round encounter. No.21 seed Kvitova advanced by walkover after Anhelina Kalinina withdrew from their scheduled second-round match due to illness.
Kvitova leads Muguruza 5-1 in their head-to-head. Their most recent meeting came in the 2021 Doha final, which Kvitova won 6-2, 6-1.
 Aryna Sabalenka def. Kaia Kanepi 2-6, 7-6(8), 6-4
In the most unpredictable match of the day, Sabalenka came back from a 6-2, 5-1 deficit and saved two match points in the second-set tiebreak to avenge her 2022 Australian Open loss to upset specialist Kanepi.
Ten of Kanepi's 15 career Top 10 wins have come at Grand Slams, including two this year over Sabalenka in Melbourne and Muguruza at Roland Garros. It seemed like another one was just around the corner as she served for the match two times in the second set.
Sabalenka, though, surged all the way back into the tiebreak, where Kanepi again took a big lead, moving ahead 5-2. But the pair jockeyed back and forth in the breaker from there, and after saving two match points -- one courtesy of a netcord-assisted pass -- Sabalenka leveled the clash.
The two power hitters slammed groundstrokes at each other in a tight third set as well, where Sabalenka served for the match for the first time at 5-4. Kanepi grabbed two break points in that game to extend the match even further, but Sabalenka held firm to wrap up the win on her third match point.
When all was said and done, Kanepi won more points, had more winners, and fired fewer unforced errors than Sabalenka. But Sabalenka stood taller at key moments down the stretch, converting her lone break point of the third set, while Kanepi was 0-for-3 during that timeframe.