Keys joins Coco Vandeweghe, who will meet KarolinaPliskova in the last eight, Sloane Stephens and Venus Williams
US Open: Madison Keys the fourth American woman in quarter-final draw where she will face world No 418 Kaia Kanepi
Madison Keys took advantage of Elina Svitolina's nerves to reach the US Open quarter-finals for the first time with a 7-6, 1-6, 6-4 win on Monday, meaning four American women are still in contention, a first since 2002.
The 15th-seeded Keys was down a break in the decider against the Ukrainian fourth seed when Svitolina lost her composure and allowed the Florida-based player to come back under the lights on Arthur Ashe Stadium.
"It's gone pretty well so far don't you think," she said on court.
"It's partially thanks to you guys, you helped me when I got down in the third set; you gave me an amazing energy boost."
The last time at least four American women were in the quarter-finals at Flushing Meadows was in 2002, with Jennifer Capriati, Lindsay Davenport, Serena and Venus Williams and Monica Seles winning their fourth-round matches.
Jennifer Brady could have been the fifth this year but she was destroyed 6-1, 6-0 by world No 1 Karolina Pliskova earlier on Monday.
Keys joined Coco Vandeweghe, who will meet Pliskova in the last eight, Sloane Stephens and Venus.
Davenport is now Keys' coach and she was seen crying in the stands after her protege hit a backhand winner down the line to seal the victory.
Keys got off to a nervous start as she quickly fell 3-0 behind but once she found her stride, Svitolina was on the back foot and the American forced a tiebreak which she easily won after earning a mini-break with a superb drop volley.
More at ease in the long rallies, Keys was, however, completely overpowered by the big-hitting Svitolina in the second set and the Ukrainian took that momentum into the third.
"I had the feeling I was hitting a wall in the second set," Keys said.
Svitolina broke for 3-2 and held for 4-2 when her nerves got the best of her.
Estonia's world No 418 Kaia Kanepi, who was once pushed to the brink of retirement by illness and crippling pain in both feet, reached the US Open quarter-finals Monday and declared: "I'm amazed I'm this good."
Kanepi, 32, became only the second qualifier to reach the last eight in New York when she defeated Russia's Daria Kasatkina 6-4, 6-4.
But this time last year, she was at home in Tallinn wondering if she would or even wanted to play tennis again despite having made five grand slam quarter-finals.
"I'm amazed that I'm this good," she said.
Her shock is well-founded.
In 2016, she appeared in just one WTA event, in Rabat, losing in the first round before a battle with the effects of Epstein-Barr virus and then plantar fasciitis in both feet forced her off tour.
But after passing her time by walking her dog Bossu, taking a vacation in Hawaii and racing cars on Finland's treacherous ice roads, she decided to try tennis once more.
"In June last year, I didn't care if I didn't play tennis again," Kanepi said.
"I just tried to live a normal life and enjoy it and slowly figuring out. But it's very important to do what you love. If you do, then things will come."
She got back into shape by training with with Estonia's 2008 Olympic discus thrower Gerd Kanter.
Once she was fit, she returned to action, playing two second-tier ITF events in Estonia and Germany while failing to qualify for Wimbledon and Bucharest.
Using a protected ranking, she entered qualifying at the US Open and has not looked back, picking up her first main draw wins in the best part of two years.
- Del Potro sets up quarter-final showdown with Federer
- Nadal and Pliskova ease into US Open quarter-finals
- Order of play Day 9: Venus WIlliams faces Petra Kvitova
"It's very tough to believe where I am now after all that has happened. I didn't expect it," she said.
She will face Keys for a place in the semi-finals.
It will be Kanepi's sixth quarter-final at the majors and second in New York after also reaching the last eight in 2010.
"Now I am a great tennis player," she said after seeing off Kastakina.
It's a feeling aided by being back in New York where she first played back in 2002.
"I have always loved being in New York. Even after I went to Hawaii, I came two days to New York just to stay in the city," she said.
"I wanted to be in the city. I like the atmosphere. I like being here. I love the courts and the climate, and I think that the courts suit my game really well."