No.9 seed Garbiñe Muguruza of Spain turned around a very unfavorable head-to-head on Wednesday when she defeated Andrea Petkovic of Germany, 6-4, 6-2, to reach the third round of the US Open.

Two-time Grand Slam champion Muguruza had lost all three of her prior meetings with former World No.9 Petkovic, but their most recent clash came at Doha in 2016, over five years ago.

Under the closed roof in Louis Armstrong Stadium, former World No.1 Muguruza finally got on the board in their rivalry with an 89-minute victory. The Spaniard moves into the third round in New York for, somewhat surprisingly, only the second time in her career.

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Muguruza is now one win away from matching her best-ever result at the US Open, a round-of-16 showing in 2017. This is the only Grand Slam event where Muguruza has not reached the final: she is the 2016 Roland Garros and 2017 Wimbledon champion, and the 2020 Australian Open runner-up.

It has still been a strong summer for resurgent Petkovic, who is back up to World No.68 in the singles rankings after recurring injury woes. Petkovic reached her first final in six years in Hamburg, and then won her first WTA singles title since 2015 in Cluj-Napoca.

Stat corner: Muguruza edged Petkovic in winners by 21 to 19, but the Spaniard kept her play cleaner with only 14 unforced errors, while Petkovic had 23.

A flurry of service breaks occurred during the second set especially, and each player had ten break points apiece in the clash. But Muguruza was more effective at those moments, converting six of her chances, while Petkovic was only 3-for-10.

Key moments: Five of Petkovic's missed break points came in only the second game of the match, and Muguruza hit her way out of danger to hold onto her serve. That crucial game was sandwiched between two service breaks in Muguruza's favor, giving her an initial 3-0, double-break lead.

Muguruza dropped serve once in the opening frame but eased on from there, and although she needed four set points in the final game, the No.9 seed took the one-set lead.

In the first game of the second set, Muguruza reached break point after a shot dribbled over the netcord, and she took that chance with a forehand winner to grab an immediate advantage. Later, five games in a row went against serve, from 3-0 to 5-2, but Muguruza's lead was never really tested as she moved to the win.

Garbiñe says: "Andrea and I, we have spent so many times, so many hours on court together training," Muguruza told the press, after her win. "We know each other a lot. [She is] one of the nicest people on tour.

"I just felt that it was difficult at some point to play, because, you get along well, but happy with my level. I think I played a very solid match from the beginning until the end."

Next up: In the third round, Muguruza will face another two-time Grand Slam champion and former World No.1: Victoria Azarenka. 

"I think it's going to be a very difficult match," said Muguruza, looking ahead. "I'm so looking forward for those type of matches. I think I had two tough matches now, and if I have to play her it's going to be another one. I think that's the best, just to go out there and play with people that are top level."

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Azarenka advances

In the match that directly followed Muguruza's on Armstrong Stadium, No.18 seed Azarenka of Belarus defeated Jasmine Paolini of Italy, 6-3, 7-6(1).

In the first meeting between the two players, last year's runner-up Azarenka fended off a spirited effort by the World No.99, as the three-time US Open finalist reached the third round for the 12th time in her career.

Former World No.1 Azarenka, a two-time Australian Open champion, was out-winnered by Paolini in the clash, by 27 to 19. But the Belarusian broke serve four times, twice as many times as Paolini, and went 15-for-15 at the net to prevail after an hour and three-quarters.

"I thought it was a pretty good level, especially the first set," Azarenka said, after her win. "I felt that in the second set I had some opportunities that I didn't close out, but she played a couple of pretty flashy moments, she took her chances. It really felt like she played really loose today.

"Overall I thought it was a pretty high-quality match, and I felt that I was happy that in the end I closed out in a strong way," Azarenka continued.

Azarenka had things mostly her way in the first set, breaking Paolini at love to lead 2-1, then earning a second break with a forehand winner to close out the one-set advantage.

However, after Azarenka took a healthy 4-2 lead in the second set, things got decidedly more competitive as Paolini used a variety of sturdy groundstrokes and off-speed plays to force forehand errors from Azarenka and pull herself into the mix. A dropshot winner gave Paolini triple break point in that game, after which she broke Azarenka to get back on serve.

Paolini boldly saved a match point in each of the 5-4 and 6-5 games, setting up a critical tiebreak. But it was there where Azarenka shone, storming through the breaker with no problems at all to set an intriguing clash with Muguruza.

Svitolina sweeps into third round

No.5 seed Elina Svitolina of Ukraine notched a 6-2, 7-5 victory over Spanish qualifier Rebeka Masarova to book her spot in the US Open third round for the sixth time in her last six appearances.

Svitolina, who reached the US Open semifinals in 2019, required an hour and a quarter of play to ease past the 22-year-old qualifier, who made her Grand Slam main-draw debut this week.

Coming off of her first title of the year last week in Chicago, Svitolina was solid as she survived both World No.231 Masarova (the 2016 Roland Garros junior singles champion) and a 30-minute rain delay, which occurred when she held break point at 5-5 in the second set.

But Svitolina was unbothered upon return, winning five of the six points after play resumed to grab the victory. Overall, Svitolina's 22 winners doubled her unforced error count, and she never faced a break point in the clash.