Pliskova had been the runner-up in 2016 and her failure to defend those points means that Wimbledon champion Muguruza will take the top ranking for the first time despite the Spaniard losing in the last 16 in New York.
Vandeweghe’s victory means that the US Open will have an all-American semi-final line-up in New York for the first time since 1981 if Madison Keys defeats Estonia’s Kaia Kanepi later Wednesday.
Venus Williams pondered 20 years of success and setbacks since reaching her first US Open final on Tuesday after moving one victory shy of another New York hard courts championship match.
The 37-year-old American, seeking her eighth Grand Slam title and third US Open crown, outlasted Czech 13th seed and two-time Wimbledon winner Petra Kvitova 6-3, 3-6, 7-6 (2).
Williams became the oldest US Open semi-finalist at 37 and the oldest in any Slam since Martina Navratilova in 1994 at Wimbledon.
US ninth seed Williams has the longest span between career Slam finals in women’s history, from the 1997 US Open to her Wimbledon loss to Garbine Muguruza in July.
Williams is set to jump into the WTA rankings top five for the first time since January 2011, her highest point since she was diagnosed with Sjogren’s Syndrome, a strength-sapping ailment.
If she beats Sloane Stephens on Thursday to reach Saturday’s final, Australian Open and Wimbledon runner-up Williams will reach her third Slam final of the year, a feat she so far has only achieved in 2002.
“Early 2000s, I mean, I had perfect health. It was great. I loved it,” Williams said. “I was fortunate to have that moment in my life. And now I’m still living my dream, and it’s amazing.”
Williams won Wimbledon and the US Open in 2000 and 2001 and took three more trophies on England grass before 2011 and Sjogren’s arrived. It took her five years before she managed to reach another Slam semi-final.
“I don’t accept limitations. So it took a while to accept some limitations,” Williams said. “But it doesn’t mean that the glass is half empty. I saw it as half full.
“Whatever I had, I had to do the best I could with that and to be the strongest I could and be reprehensible for each and every shot I hit.”
Q. Could Venus win the next two matches?
PETRA KVITOVA: I think she can. I hope so, actually (smiling). #USOpen
— WTA Insider (@WTA_insider) September 6, 2017
Williams pondered how many WTA players have had to overcome setbacks and return to champion form and the inspiration it can provide.
“Sport is a little microcosm of life and it shows the human spirit, just being out there on the court, fighting against all odds. If you’re down, you keep going,” Williams said. “Great champions came back from injuries or circumstances they could never have planned for. It’s very encouraging for people to watch… You never know whose life you’ll touch just by being your best.”
Williams doesn’t believe in comparing matches or performances since what is needed for victory changes with every foe.
“I’m not into the whole best-match thing. It’s about winning the match you’re in,” she said. “Doesn’t matter whether you’re playing well or not playing well. It’s about figuring out how to win.
“If you’re out there thinking you have to play your best match every time, you’re not going to win these events. That’s too much of a high expectation.”
There are high expectations of another sort at the edge of her thoughts, with Hurricane Irma forecast to strike near her Florida home at the weekend.
“I haven’t watched Irma closely but perhaps I should know more,” Williams said. “I have a lot of family and important people in Florida and my whole life is there.”
But first, she will turn her attention to Stephens, who won their only prior meeting in the first round of the 2015 French Open.
“I have to focus on what’s happening on my side of the court, make evaluations when I’m out there in terms of strategy and see what’s working,” Williams said.
Spanish 12th seed Pablo Carreno Busta, who has not dropped a set at the US Open, advanced to his first Grand Slam semi-final on Tuesday by defeating Argentine 29th seed Diego Schwartzman 6-4, 6-4, 6-2.
Carreno Busta, the first player to face four qualifiers in any Grand Slam, booked a Friday semi-final against the winner of a night match between South African 28th seed Kevin Anderson and 17th-seeded American Sam Querrey, whose first Slam semi-final in was July at Wimbledon.
“Incredible,” Carreno Busta said. “It’s something that I always dreamed about but something I never thought was going to arrive here. It’s a great feeling.”
While legends Roger Federer and Rafael Nadal are each one win from meeting for the first time at the US Open in a potentially epic semi-final on the other half of the draw, this side is guaranteed to produce a first-time Slam finalist.
“It would be fantastic to play him in the final,” Carreno Busta said of facing countryman Nadal in the final. “But we have to play step by step.”
Carreno Busta broke at love to open the match and again to lead 5-2 on the way to taking the first set in 38 minutes.
After an early exchange of second-set breaks, Carreno Busta broke to 5-4 and held to claim the set, then broke at love on a double fault to open the third set.
The Spaniard denied Schwartzman on a break point in the fourth game, and on 6-of-8 in the match, then broke again in the seventh game before holding for victory in just under two hours.
Schwartzman, at 5ft 7in (1.70m), was the shortest Slam quarter-finalist since same-height Peruvian Jaime Yzaga at the 1994 US Open.
— US Open Tennis (@usopen) September 5, 2017
Seven-time Grand Slam champion Venus Williams, this year’s Australian Open and Wimbledon runner-up, faces two-time Wimbledon champion Petra Kvitova later for a berth in Thursday’s women’s semi-finals.
US ninth seed Williams, the oldest women’s entrant at age 37, seeks her third US Open crown after 2000 and 2001.
She would be the oldest women’s Grand Slam semi-finalist since Martina Navratilova at Wimbledon in 1994 and the eldest in US Open history.
Kvitova, who leads their career rivalry 4-1, is battling back following a five-month absence after injuring her left hand when attacked by a knife-wielding home intruder last December.
The winner will face either 83rd-ranked American Sloane Stephens, who missed 11 months with a left foot injury before returning at Wimbledon, or Latvian 16th seed Anastasija Sevastova.
Stephens hopes to match her best Slam run to the 2013 Australian Open semis while Sevastova has matched her best Slam run from last year in New York.
Four American women, also including Madison Keys and CoCo Vanderweghe, have reached the quarter-finals for the first time since 2002 and they could produce the first all-US semi-finals in New York since 1981.
Estonian 418th-ranked qualifier Kaia Kanepi has matched Barbara Gerken from 1981 for the deepest run by any US Open women’s qualifier. No male or female qualifier has ever reached a US Open semi-final.
What began as an eight-woman fight for the world number one ranking at the US Open is down to two.
Czech Karolina Plishkova, the reigning number one and last year’s US Open runner-up, must reach this year’s final or lose the top spot to already-ousted Garbine Muguruza, the reigning Wimbledon champion.