|Venue: Flushing Meadows, New York Dates: 28 Aug-10 Sept|
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Madison Keys made it four American women in the US Open quarter-finals with victory over fourth seed Elina Svitolina.
Keys, seeded 15th, won 7-6 (7-2) 1-6 6-4, ending Svitolina's hopes of becoming world number one.
The Ukrainian needed to at least reach the semi-finals to have a chance of topping the rankings.
Keys joins compatriots Coco Vandeweghe,Venus Williams and Sloane Stephens in the last eight.
Williams and Stephens play their quarter-finals on Tuesday.
It is the best performance by American women since Venus and Serena Williams, Lindsay Davenport, Jennifer Capriati and Monica Seles all reached the last eight in 2002.
Karolina Pliskova must now make the final to keep the world number one ranking from Spaniard Garbine Muguruza, and the Czech cruised into the quarter-finals.
The top seed, 25, needed only 46 minutes to beat American world number 91 Jennifer Brady 6-1 6-0 on Arthur Ashe Stadium.
Pliskova will next face 20th seed Vandeweghe, who beat 2015 French Open finalist Lucie Safarova 6-4 7-6 (7-2).
They were joined in the last eight by Estonian Kaia Kanepi, who beat Russia's Daria Kasatkina 6-4 6-4 to reach her first US Open quarter-final since 2010.
The 32-year-old, ranked 418 after injury problems, is the first qualifier since 1981 to reach the last eight and she faces Keys next.
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'Pliskova has to worry about me'
Vandeweghe used her powerful forehand to outmuscle Safarova and was more consistent than her Czech opponent, who missed three break-point opportunities at 4-4 in the first set.
The American was a US Open junior champion as a teenager but had failed to make it past the second round in her previous eight senior appearances at Flushing Meadows.
She will now face Pliskova, who needs to reach the final to have a chance of retaining her world number one ranking.
"Pliskova plays a pretty big game. She holds serve very quickly and makes it difficult to get a rhythm," Vandeweghe said.
"But she also has to worry about me. I do the same thing on my service game."
Pliskova has had a mixed tournament so far but was efficient against Brady, hitting 23 winners to the American's six, and dominating with her first serve.
Brady won only 22 points, compared to Pliskova's 55, and struggled for rhythm.
"I felt like it's even faster than the time on the board," said Pliskova.
"She didn't play well. I was just trying to stay in my zone as long as I can and didn't wait for the moment where she can maybe get back in the match."
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