American 20th seed CoCo Vandeweghe reached the US Open semi-finals on Wednesday with a 7-6 (7/4), 6-3 win over Karolina Pliskova as the Czech player lost her world number one ranking to Garbine Muguruza.
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.