Madison Keys chases down a shot in the second set of a quarterfinal match against Kaia Kanepi, of Estonia at the U.S. Ope Wednesday, Sept. 6, 2017. Keys' straight-set win completed an all-United States semifinal round.

NEW YORK — Madison Keys completed the clean sweep for American women, giving the host country all four U.S. 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 during a 6-3, 6-3 victory over 418th-ranked qualifier Kaia Kanepi of Estonia that lasted only 69 minutes Wednesday night.

That 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 — and No. 9 seed Venus Williams meets 83rd-ranked Sloane Stephens.

“We’re going to have four American women playing tomorrow, and that’s pretty awesome,” Keys told the Arthur Ashe Stadium crowd, drawing a roar of approval.

Williams, whose seven major championships include the 2000 and 2001 U.S. Opens, and Stephens won quarterfinals Tuesday.

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

Not since 1981 have there been four American women in the final four at the U.S. 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 members of the remaining trio 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 white towel over her head during changeovers and dropped to 0-6 in Grand Slam quarterfinals.

Keys set the tone in the opening game: ace at 108 mph, ace at 105 mph, service winner at 117 mph, service winner at 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 this is where I would be, right before Wimbledon, I wouldn’t have believed you.”

U.S. Open Results

By The Associated Press

NEW YORK — Results Wednesday from the U.S. Open at USTA Billie Jean King National Tennis Center (seedings in parentheses):

Men’s Singles

Quarterfinal

Rafael Nadal (1), Spain, def. Andrey Rublev, Russia, 6-1, 6-2, 6-2.

Women’s Singles

Quarterfinal

CoCo Vandeweghe (20), United States, def. Karolina Pliskova (1), Czech Republic, 7-6 (4), 6-3.

Madison Keys (15), United States, def. Kaia Kanepi, Estonia, 6-3, 6-3.