NEW YORK - World number one Iga Swiatek was sent crashing out of the US Open on Wednesday by Jessica Pegula who moved into her first Grand Slam semi-final.
Sixth-ranked Pegula triumphed 6-2, 6-4 and will face Karolina Muchova of the Czech Republic for a place in Saturday's final.
If the 30-year-old gets through that she could set-up an all-American final if Emma Navarro stuns world number two Aryna Sabalenka in Thursday's other semi-final.
Victory ended Pegula's run of losing all six Grand Slam quarter-finals in which she had played and extended her streak to 14 wins in 15 matches on US hard courts this summer.
"Finally I can say I'm a semi-finalist. I lost so many of these damn things," said Pegula after her fourth career win against Swiatek.
"Thanks to the crowd. I sent over a 65mph second serve (on a third match point) because I was so tight.
"I did everything I could to not get frustrated. I took advantage of some things she was not doing so well and just rode that momentum."
Pegula raced into a double break in the first set as 2022 US Open winner Swiatek was plagued by mistakes.
By the end of the opener she had hit just three winners and committed 19 unforced errors as her game fell apart under the Arthur Ashe Stadium lights.
It was a dramatic slump for four-time French Open champion Swiatek who hadn't faced a single break point in her three preceding matches at the tournament.
Pegula turned the screw for a 2-1 lead in the second before Swiatek retrieved the break.
But the Polish star couldn't capitalise and was broken again when a forehand error handed Pegula a 4-3 edge.
The American claimed victory on a third match point when Swiatek went wide again for her 41st and final unforced error of the night.
Unseeded Muchova earlier eased into her second successive US Open semi-final by sweeping past Beatriz Haddad Maia 6-1, 6-4.