CoCo Vandeweghe has five wins at this U.S. Open this year, more than the she had in the previous eight Opens she played. That can mean only one thing: She’s made it to the semifinals.

She reached that lofty summit Wednesday by beating the world’s No. 1 player. She did it looking as if she belonged, with a steadiness that had not been characteristic of her game and a doggedness that served her oh so well.

The 7-6 (4), 6-3 victory over Karolina Pliskova at Arthur Ashe Stadium made her the third of four American women to reach the semifinals, where she will face Madison Keys Thursday night. With a bright outlook and a new coach in Pat Cash, Vandeweghe is on the roll of her life. When match point was won, she collapsed to her knees.

“I think it’s a lot of validated work,” Vandeweghe said. “I think what really was going through my mind in that moment was I’m a big believer that my grandparents are still with me. It was more just looking up and feeling the love of everything that was going on.”

In the first and second sets Vandeweghe was up a break, only to give it up. Vandeweghe wears her emotions on her sweatbands, and after a double fault in the first set, she let her racket know about it, ending its functional life with death by hardcourt. She went on to be broken with the score at 4-all.

But it was particularly telling when she was serving the 10th game at 4-5 and Pliskova gained a set point. Vandeweghe forced an error to save it and held. With Pliskova serving first in the tiebreak, Vandeweghe hit a big forehand to take the lead and was never threatened in taking the first set.

In the second set Vandeweghe earned a break in the fourth game and handed it right back in the fifth. One game later Vandeweghe recaptured the break and the lead. Serving for the match in the ninth, she fought off a break point. Two deuce points later she was in the semifinals.

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She talked to Cash immediately after the win. Cash, known as an intense, steely competitor, seems to have planted that message in Vandeweghe.

”I think the biggest thing is channeling my intensity and tenacity out onto the court and putting it into a singular focus,” Vandeweghe said. “I think that’s probably one of the biggest things he’s implemented into my regimen.”

Pliskova didn’t see anything new in Vandeweghe, just better execution.

“Her game doesn’t surprise me at all,” Pliskova said. “I think there was no changes. Even when she changed coach, I think, for me, nothing change.”

Vandeweghe felt a difference Wednesday in the way she made Pliskova play the points and tried not to give anything away.

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“I think my best asset today was making her continually play on her service games,” Vandeweghe said. “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.”

And with that attitude, Vandeweghe will now be serving for a spot in the U.S. Open final.