Madison Keys stuns Jessica Pegula; Aryna Sabalenka powers into ...

NEW YORK -- Aryna Sabalenka is going to be the No. 1 player in the WTA rankings next week, replacing Iga Swiatek. That much is certain. The way Sabalenka is playing at the moment, she might very well supplant Swiatek as the US Open champion, too.

In Sabalenka's first match since being assured of rising to the top of women's tennis, she showed off the power-based game that allows her to dominate so many opponents, overwhelming No. 13 seed Daria Kasatkina 6-1, 6-3 on Monday night in Arthur Ashe Stadium to advance to her fifth consecutive major quarterfinal.

"All this year, I've been pushing myself so hard to reach this goal," Sabalenka said of getting to No. 1. "It really means a lot for me. It means a lot for my family. It's crazy. It's unbelievable."

After the top-seeded Swiatek lost in the fourth round Sunday night, hours after No. 4 Elena Rybakina bowed out, No. 3 Jessica Pegula and No. 5 Ons Jabeur -- who was the runner-up in New York a year ago -- were both defeated Monday.

That left Sabalenka as the only one of the top five women remaining in the bracket.

She will play No. 23 Zheng Qinwen on Wednesday for a spot in the semifinals. The other quarterfinal on the bottom half of the draw will be Wimbledon champion Marketa Vondrousova against No. 17 Madison Keys, the US Open runner-up in 2017.

Keys stunned third-seeded Pegula 6-1, 6-3 in an all-American clash at Arthur Ashe Stadium on Monday, reaching the US Open quarterfinals for the first time since 2018.

Keys crashed out of the first round at Cincinnati last month but appeared right at home on the New York hard courts, where she was runner-up in 2017, as she overwhelmed her opponent with 21 winners.

Pegula beat Keys in their only previous meeting last year and was considered one of the U.S.'s brightest hopes after winning the Montreal title last month.

However, on Monday she lacked her usual firepower and finesse.

"I've had so many amazing moments in New York," said Keys, who is playing in her 12th US Open main draw.

"Being able to at any moment come back from any difficult positions I've been in matches has been amazing."

Keys broke her opponent's serve with a backhand winner in the second game of the first set and broke Pegula again on the fourth try in game six.

Pegula was clearly off her game and threw her racquet down in frustration as she helped Keys to the break with a double fault and a backhand error in the fifth game of the second set.

Pegula broke back immediately in the sixth game but Keys kept her cool, retaking the lead as she broke her opponent's serve in the seventh game.

Keys, who counts Pegula as a close friend, pumped her fist in a subdued celebration as the top-ranked American dropped her serve again when she sent a forehand shot into the net on match point.

"It's always tough having to play a friend ... when we get on the court it's all business," Keys said in a courtside interview.

Meanwhile, the quarterfinals on the top half of the women's bracket will be played Tuesday: No. 6 Coco Gauff vs. 2017 French Open champion Jelena Ostapenko, and No. 10 Karolina Muchova vs. No. 30 Sorana Cirstea.

Zheng, a 20-year-old from China, was responsible for eliminating Jabeur, who's been sick, by the score of 6-2, 6-3 to reach a Grand Slam quarterfinal for the first time.

The Associated Press and Reuters contributed to this story.