While the other big names fell around her on a day of upsets, Maria Sharapova extended her perfect record with victory over Jelena Ostapenko at Flushing Meadows.
Women's US Open, Saturday review (round three)
Defending champion Sloane Stephens is the sole remaining top-six seed left in the women's singles at the US Open after a day of upsets at Flushing Meadows.
Wimbledon champion Angelique Kerber and fifth seed Petra Kvitova both fell on Louis Armstrong Stadium, which is rapidly establishing itself as a graveyard of champions, while sixth seed Caroline Garcia also lost.
Kvitova was the last victim of the day, the two-time Wimbledon champion overpowered by the hottest player of the moment: 20-year-old Aryna Sabalenka.
The Belarusian was not ranked highly enough to get into the tournament 12 months ago but has soared into the top 20 and won her first WTA Tour title in New Haven on the eve of the tournament.
She has now won 12 of her last 13 matches, and Sabalenka said: "I am so happy with that. I didn't say to myself, 'I have to win this 6-1'. I was like,'Keep fighting, keep going'. Everything was going in."
Kvitova struggled on serve, hitting 10 double faults, but praised Sabalenka, saying: "I had my chances in the first set. I took it then I lost it again then she took it all the way. After that she just played really fearless and really aggressive, which I didn't have the answer for."
The Czech has won five WTA titles this season but only four matches across the four grand slams.
She said: "The French Open I was a bit tired. The Australian Open and Wimbledon were similar, I didn't really play fearless, I was a bit passive and I didn't have the confidence that I needed and I put a lot of pressure on myself.
"I really tried to change it for this grand slam, which I think I did quite well. Hopefully I find a way. I just need to work on it."
Kerber's exit, joining Simona Halep and Caroline Wozniacki, means there will be four different grand slam champions for the second year in a row.
Kerber was the last woman to collect two slam titles in a season, winning the Australian and US Opens in 2016 before a dramatic slump last year.
She has been resurgent under the guidance of Wim Fissette, capped by her brilliant victory over Serena Williams at Wimbledon, and had reached at least the quarter-finals at the previous three slams.
But here she found Dominika Cibulkova a step too far, the Slovakian winning 3-6 6-3 6-3.
Kerber said: "I had my chances, but I couldn't take them, especially in the third set. I was not able to play my best tennis in the important moments. She was going for it, and she hit the balls really good and played the winners when she has to."
While the other big names fell around her, Maria Sharapova remained the queen of the night session, extending her perfect record with victory over Jelena Ostapenko.
The 2006 champion has played 23 times under the lights at Flushing Meadows and won on each occasion.
She got a helping hand this time from 10th seed Ostapenko, last year's French Open champion, who hit 40 unforced errors in just 17 games to go down 6-3 6-2.
Sharapova said: "I don't remember how old I was when I played my first night match, but I'm sure I was young enough to still be intimidated by the city and the lights and the atmosphere, the noise, as anyone that's quite young would be.
"But I really turned that around. I think I thrive on that. I love the atmosphere. I love that they know how to cheer hard."
Cibulkova next plays last year's runner-up, Madison Keys, who avoided an upset by fighting from a set down to defeat Aleksandra Krunic 4-6 6-1 6-2.
Another upset saw Cincinnati champion Kiki Bertens beaten 7-6 (7/4) 2-6 7-6 (7/1) by Czech teen Marketa Vondrousova.
Vondrousova next faces Ukraine's Lesia Tsurenko, who followed up her victory over Wozniacki by beating Katerina Siniakova 6-4 6-0.
Naomi Osaka has been the most efficient player over the first three rounds and the 20-year-old Japanese-American, who next meets Sabalenka, blasted her way into the last 16 of grand slam for only the second time with a 6-0 6-0 victory over Aliaksandra Sasnovich.
