Pliskova needed to reach the final to hang on to the No. 1 ranking, but defeat means she will be replaced by Muguruza in the new standings next week.
Before the match, Vandeweghe said that it would be a match of “first-strike” tennis between two of the best servers and biggest hitters in the game, and the American proved the more clinical.
She won 56% of the rallies under four strokes, which accounted for the vast majority as both women looked to back up heavy serves with quick winners.
Vandeweghe, goes on to face compatriot Madison Keys in the last four in New York.
Pliskova came into the match with a tournament-high 31 aces, but the was limited to only two against Vandeweghe as she struggled to dictate the pace of the game.
When asked how it felt to lose the top ranking barely two months after achieving it, she said – “I mean, I don’t care. I don’t think something is going to change if you are number two. Like, I don’t see any difference between this. So for me, no changes.
Madison Keys’ victory over Kaia Kanepi ensured the first all-American semi-final line-up at the US Open since 1981 with Venus Williams facing Sloane Stephens.
During her on-court interview, Vandeweghe said “When I won this event as junior at 16 I always dreamed of being on the main stage. It is a process and here I am. I couldn’t wish for anything better.”