Madison Keys of the United States chases down a shot during the second set of her quarterfinal victory against Kaia Kanepi of Estonia at the US Open on Wednesday. KATHY WILLENS/AP

NEW YORK - Madison Keys completed a clean sweep for American women on Wednesday, giving the host country all four US Open semifinal spots for the first time in 36 years.

The 15th-seeded Keys served impeccably, controlled groundstroke exchanges from the baseline and was never in trouble en route to a 6-3, 6-3 victory over 418th-ranked qualifier Kaia Kanepi of Estonia that took just 69 minutes.

It came several hours after 20th-seeded CoCo Vandeweghe's 7-6(4), 6-3 elimination of 2016 runner-up and top-seeded Karolina Pliskova of the Czech Republic.

Pliskova's loss means she will be replaced at No 1 in the rankings by Wimbledon champion Garbine Muguruza.

On Thursday, Keys faces Vandeweghe - with the winner reaching her first Grand Slam final - while No 9 seed Venus Williams meets 83rd-ranked Sloane Stephens.

"Oh my God, it feels so good. We have so many Americans to talk about in the last days of the US Open," Keys said.

"I can't tell you how many times I have sat in this chair and had to hear, you know, how horrible tennis is in America."

Stephens and Williams, whose seven major championships include the 2000 and 2001 US Opens, won their quarterfinals on Tuesday.

"American tennis is headed in the right direction," said Stephens, seeking her debut in a major final.

Not since 1981 has there been four American women in the final four at the US Open, when the quartet was champion Tracy Austin, runner-up Martina Navratilova, Chris Evert and Barbara Potter.

It hadn't happened at any Grand Slam tournament since Wimbledon four years after that.

While Williams is 37, the oldest semifinalist in tournament history, the other three are all in their 20s.

Keys, 22, had a rough start to 2017, missing the first two months after offseason surgery on her left wrist, and then had another procedure in June because of lingering pain.

She was terrific against Kanepi, who sat with a towel over her head during changeovers and dropped to 0-6 in Grand Slam quarterfinals.

Keys set the tone in the opening game, firing aces of 108 and 105 mph and service winners of 117 and 112 mph. She wound up with eight aces, part of a 23-8 in total winners.

"This means the world to me," said Keys, also a semifinalist at the 2015 Australian Open. "If someone told me, right before Wimbledon, that this is where I would be, I wouldn't have believed it."

The 25-year-old Vandeweghe, niece of former NBA player and current league executive Kiki Vandeweghe, reached her first Grand Slam semifinal at the Australian Open in January.

She was the junior champion in New York in 2008, but never had success in the main draw until now. Of her previous eight appearances, half ended in the first round, half in the second.

One difference this time at the US Open: Vandeweghe switched coaches midway through the season, teaming up in June with 1987 Wimbledon champion Pat Cash, who on Tuesday was nominated for induction into the International Tennis Hall of Fame.

"The biggest way in which Pat has helped is by channeling my intensity and tenacity out onto the court and putting it into a singular focus," said Vandewghe.

How?

"I don't really know. Maybe it's like some Jedi mind trick," said Vandeweghe, who cracked a racket when she slammed it to the ground after a second consecutive double-fault in the opening set.

Regardless, pretty much everything she did worked against Pliskova, who leads the tour in aces in 2017 but found her top means of attacking opponents neutralized on Wednesday.

Vandeweghe wound up with more aces, 5-2, and even produced three service winners.

"My best asset today was making her continually play on her service games. Whether it was not a great return that just got over the net, I know as a big server it's really annoying when your serve keeps coming back," Vandeweghe said.

"I know that's what my main focus was - just to get it back, not have her have a free point too easily."

Pliskova did not exactly heap praise on her opponent afterward.

"I was not playing my best tennis this tournament," she said. "She can play much worse than she was playing today, and I can play much better than I was playing today. I didn't feel the best."

Pliskova, from the Czech Republic, also offered this assessment of Vandeweghe: "She just has one plan, so either it's working or it's not."

Associated Press